title: Variable rampUp with Gatling
body: <p>I try to make an injection with a variety of "breaks" and "atOnceUsers".
  I didn't found a nice solution on the documentation for that.</p>
  
  <p>My approach was to create a function called "getNextNumber()" with a local counter, to increase the number of "atOnceUsers", but the function was only called once at the beginning.</p>
  
  <p>Any ideas?</p>
  
  <p>My code:</p>
  
  <pre><code>class TestCombinationGetFiles extends Simulation {
      var counter: Int =1 
  
      def getNextNumber():Int = {
        counter+= 1
        return counter
      }     
  
    val Get20Files = scenario("get20Files")
     .feed(UuidFeeder.feeder)
     .exec(WebAuth.AuthenticateUser)
     .pause(30)
     .exec(WebCloudContent.GoToTestFolder20)
  
   val Get10Files = scenario("get10Files").feed(UuidFeeder.feeder)
    .exec(WebAuth.AuthenticateUser)
    .pause(15)
    .exec(WebCloudContent.GoToTestFolder10)
  
   val loadFolder20TestRamp =            
    scenario("loadFolder20TestRamp").exec(WebAuthSwisscom.AuthenticateUser,             
     WebCloudContentSwisscom.GoToTestFolder20)    
  
   setUp(Get20Files.inject(
      splitUsers(36) into( 
          atOnceUsers(getNextNumber())) 
          separatedBy(30 seconds)) 
  
          /* messy Code with correct functionality
          atOnceUsers(1),
          nothingFor(30 seconds),
          atOnceUsers(2),
          nothingFor(30 seconds),
          atOnceUsers(3),
          nothingFor(30 seconds),
          atOnceUsers(4),
          nothingFor(30 seconds),
          atOnceUsers(5),
          nothingFor(30 seconds),
          atOnceUsers(6),
          nothingFor(30 seconds),
          atOnceUsers(7),
          nothingFor(30 seconds),
          atOnceUsers(8),
          nothingFor(30 seconds))
          */
      ,
      Get10Files.inject(
          splitUsers(16) into( 
             atOnceUsers(1)) 
             separatedBy(15 seconds)) 
     ).protocols(WebSetUp.httpProtocol)
  }
  </code></pre>