Fix parsing of github PR url

We parse the owner, project and PR number of a github PR out of the
PR URL.  When using github enterprise, the path preceding
$org/$repo/pulls/$number in the URL may contain some extra stuff which breaks
the parsing here. This fixes the parsing to parse that info from the end of
the string regardless.

Change-Id: Ifdf03e8aa399bf6e56ff8711c22e03c1584649df
1 file changed