title: Define environment variables with agent none in Jenkins pipeline
body: <p>I have a pipeline where I do:</p>
  
  <pre><code>#!/bin/groovy
  
  pipeline {
      agent none
      environment {
          agent any
          INSTANCE_NAME = "Jenk"
    }
  
    stages {
      stage("Print Debug Vars"){
          steps {
              sh 'echo "INSTANCE_NAME is $INSTANCE_NAME"'
          }
      }
  
      stage("Git Checkout") {
          agent { label 'docker' }
          steps  {
              // ...
              }
        }
      }
  
      stage("Ansible Galaxy"){
          agent { label 'ansible' }
          steps  {
              // ...
              }
      }
    }
  }
  </code></pre>
  
  <p>Problem I that if I put </p>
  
  <pre><code>agent any
  </code></pre>
  
  <p>in environment section, it says:</p>
  
  <pre><code>WorkflowScript: 6: "agent any" is not a valid environment expression. Use "key = value" pairs with valid Java/shell keys. @ line 6, column 5.
         agent any
         ^
  
  WorkflowScript: 5: Expected name=value pairs @ line 5, column 5.
         environment {
         ^
  </code></pre>
  
  <p>And if I don't put it, I get:</p>
  
  <pre><code>Required context class hudson.Launcher is missing
  Perhaps you forgot to surround the code with a step that provides this, such as: node
  [Pipeline] // withCredentials
  [Pipeline] }
  [Pipeline] // withEnv
  [Pipeline] End of Pipeline
  org.jenkinsci.plugins.workflow.steps.MissingContextVariableException: Required context class hudson.Launcher is missing
      at org.jenkinsci.plugins.workflow.steps.StepDescriptor.checkContextAvailability(StepDescriptor.java:253)
      at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:179)
      at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:126)
      at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:108)
      at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:48)
      at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
      at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
      at com.cloudbees.groovy.cps.sandbox.DefaultInvoker.methodCall(DefaultInvoker.java:18)
      at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withCredentialsBlock(jar:file:/var/jenkins_home/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:239)
      at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withCredentialsBlock(jar:file:/var/jenkins_home/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:238)
      at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.call(jar:file:/var/jenkins_home/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:76)
      at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.inWrappers(jar:file:/var/jenkins_home/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:346)
      at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.inWrappers(jar:file:/var/jenkins_home/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:345)
      at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.call(jar:file:/var/jenkins_home/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:75)
      at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withEnvBlock(jar:file:/var/jenkins_home/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:218)
      at ___cps.transform___(Native Method)
      at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:57)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:109)
      at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:82)
      at sun.reflect.GeneratedMethodAccessor279.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:498)
      at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
      at com.cloudbees.groovy.cps.impl.ClosureBlock.eval(ClosureBlock.java:46)
      at com.cloudbees.groovy.cps.Next.step(Next.java:74)
      at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:154)
      at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
      at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:33)
      at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:30)
      at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.GroovySandbox.runInSandbox(GroovySandbox.java:108)
      at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:30)
      at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:165)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:328)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$100(CpsThreadGroup.java:80)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:240)
      at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:228)
      at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:64)
      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
      at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:112)
      at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
      at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at java.lang.Thread.run(Thread.java:745)
  </code></pre>
  
  <p>How should I do it ?</p>