ensure we only compare what we need to

When comparing fingerprints, the last section is host specific - but
it's irrelevant. So we chop that bit off, and ensure that the actual
algorithm and public key still match.
Merge pull request #22 from thommay/compare_less_greedily

only compare the relevant bits of the ssh key fingerprint
Bump revision to 0.5.3
Fix fog_key_pair < 2.0 so that it can actually test for pkcs fingerprints on AWS
Bump revision to 0.5.4