Attach labels instead of erroring on creation if label already exists
Attach labels instead of erroring on creation if label already exists

If a label already exists, don't error out when trying to post to the
job_templates/n/labels endpoint, instad just lookup the ID and attach
it. This is primarily to benefit the UI, but in general seems like a
good behavior for this endpoint anyways.

 Fixes #2135

wwitzel3/awx,snahelou/awx,snahelou/awx,snahelou/awx,snahelou/awx,wwitzel3/awx,wwitzel3/awx,wwitzel3/awx