Exception handling to always release work units

[AlanCoding]

Connect ansible#9154

I'm developing a process for testing these

• first we run sleep playbook https://github.com/ansible/test-playbooks/blob/master/sleep.yml
• while it's sleeping, shell into server, manually receptorctl work cancel <unit id> for that job
• after the job is reported as an error, then we check the work list to see that it's not there

I believe we will, eventually, need a new setting like AWX_CLEANUP_PATHS like AWX_RELEASE_WORK_UNITS to turn this off... or maybe just abuse the cleanup path setting?