Add check for multiple artists in MusicBrainz search
- It's a hack now - we assume only one of the artists returned
  is actually popular, so we iterate through each musicbrainz artist id
  and return the first one that results in a valid response from a setlist.fm search
- Need a better solution
100% coverage. Some tests are failing.
Merge pull request #23 from tihuan/test/increase_coverage_for_all

100% coverage. Some tests are failing.
Merge pull request #22 from raderj89/chore/musicbrainz-multiple-artists

Add check for multiple artists in MusicBrainz search