Description of problem: 

- Changing concurrency level while executing Ansible jobs fail with NoMethodError: undefined method `[]' for nil:NilClass
- The action on the servers themselves finishes correctly, the only issue is Satellite reporting the job as failed

Version-Release number of selected component (if applicable):

- satellite-6.6.0-7.el7sat.noarch

How reproducible: 100%


Steps to Reproduce:
1. Monitor > Jobs > Run job > (default) Ansible commands | Run command > fill search query to 'name ~ test-rhel*' > hit 'Refresh' button to ensure it matches the right hosts > complete Command field to 'uname -a'  -> set concurrency level field to 1 -> hit Submit
2. If we run a job on a list of 55 hosts with default concurrency level (unset, all jobs launched simultaneously), job finish detection works fine and all are maked as OK.
3. If we run a job on the same 55 hosts with concurrency level = 5 (or 10 or whatever); the first batch of servers works ok, but any other server after that, their job is executed on the target machine but marked as Failed on Satellite.

Actual results:

- Ansible jobs fail with "Error:NoMethodError undefined method `[]' for nil:NilClass"

Expected results:

- Ansible REX jobs should succeed.