mutagen: switch to setup-py (python apiv2), bump to 1.22

Also, do some initial work towards running tests. They work for me
when run manually, but inexplicably fail with a floating-point
exception in flac when run by paludis in sydbox.

Change-Id: Ic2cc216b3708a6fecbfeff5082f01e8e4f438d6a
mutagen: common-metadata.exlib: Whitespace