Fix gitian-build.py --verify option
Fix gitian-build.py --verify option

The gitian-builder/bin/gverify script returns the exit code 1 if a
signature verification ends with 'BAD SIGNATURE' or 'MISMATCH' by
design. This commit allows to see the verification results for all
signatures without a premature fail of the gitian-build.py script.

peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin