title: How to retrieve a value from Airflow XCom pushed via SSHExecuteOperator
body: <p>I have the following DAG with two SSHExecuteOperator tasks. The first task executes a stored procedure which returns a parameter. The second task needs this parameter as an input.</p>
  
  <p>Could please explain how to pull the value from the XCom pushed in task1, in order to use it in task2?</p>
  
  <pre><code>from airflow import DAG
  from datetime import datetime, timedelta
  from airflow.contrib.hooks.ssh_hook import SSHHook
  from airflow.contrib.operators.ssh_execute_operator import SSHExecuteOperator
  from airflow.models import Variable
  
  default_args = {
    'owner': 'airflow',
    'depends_on_past': False,
    'start_date': datetime.now(),
    'email': ['my@email.com'],
    'email_on_failure': True,
    'retries': 0
  }
  
  #server must be changed to point to the correct environment, to do so update DataQualitySSHHook variable in Airflow admin
  DataQualitySSHHook = Variable.get('DataQualitySSHHook')
  print('Connecting to: ' + DataQualitySSHHook)
  sshHookEtl = SSHHook(conn_id=DataQualitySSHHook)
  sshHookEtl.no_host_key_check = True 
  
  #create dag
  dag = DAG(
    'ed_data_quality_test-v0.0.3', #update version whenever you change something
    default_args=default_args,
    schedule_interval="0 0 * * *",
    dagrun_timeout=timedelta(hours=24),
    max_active_runs=1)
  
  #create tasks
  task1 = SSHExecuteOperator(
    task_id='run_remote_sp_audit_batch_register',
    bash_command="bash /opt/scripts/data_quality/EXEC_SP_AUDIT_BATCH.sh 'ED_DATA_QUALITY_MANUAL' 'REGISTER' '1900-01-01 00:00:00.000000' '2999-12-31 00:00:00.000000' ", #keep the space at the end
    ssh_hook=sshHookEtl,
    xcom_push=True,
    retries=0,
    dag=dag)
  
  task2 = SSHExecuteOperator(
    task_id='run_remote_sp_audit_module_session_start',
    bash_command="echo {{ ti.xcom_pull(task_ids='run_remote_sp_audit_batch_register') }}",
    ssh_hook=sshHookEtl,
    retries=0,
    dag=dag)
  
  #create dependencies
  task1.set_downstream(task2)
  </code></pre>