When receiving a status or checks event we need to find the
corresponding pull request to that event. Github stores the status on
the head commit of a pr and not on the pr itself which leads to
problems if multiple prs exist with the same head but different target
branches. Therefore zuul errors out when more than one pr is found for
that event. However the github search also returns all prs that
contain the sha we search for but have a different head which leads to
the same error as if we had two conflicting prs. This can be solved by
delaying the error and filtering the pr bodies for the head sha first.
Change-Id: Iadafd3cf68a742941e9189e84fca594bc3394084
0093aabd4e