Pipeline processing broken because of race condition

Recently merged !6650 (merged) introduced problem with asynchronous job being deployed when around_transition still held transaction, which caused race condition that prevented pipeline status to change in a proper way.

For details see https://github.com/pluginaweek/state_machine/issues/191

We already had simiar problem that was solved in f68acbac.

MR with the fix: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6736

/cc @ayufan @dzaporozhets