non-SLURP branches are EOL'd in case they reach their end of maintained
phase. This could produce a situation when a patch is merged in a
non-SLURP branch that was deleted in the meantime and it's further
backports fail on gate with backport validator as the hash of the
non-SLURP version of the patch is not on any branch.
This patch fixes the above issue as follows: in case a hash is not
found on any branch, then it checks if it can be found under any *-eol
tag and only fails if there is not found either.
Change-Id: I56705bce8ee4354cd5cb1577a520c2d1c525f57b
e383b46545