The release-approval pipeline implemented a nice infinite loop as
it was triggered by all comment-added events, and Zuul is posting one
every time the job runs.
Add a regexp to exclude comment-added events from the 'zuul' user.
Also since patchset-created actually does not trigger comment-added,
it needs to be specified separately (in order to approve releases
proposed by the PTL themselves).
Change-Id: I0f8b8526adaa83876ff92a98500d35c70cc23174
7d6c978e70