Currently, the code in rpmautospec.release (and by extension, rpmautospec.process_distgit) queries Koji for information about existing builds. When run in the mock chroot, it should use the tags in the repository instead.

Background:

• Currently the code would attempt to contact the Koji prod instance from within the chroot, because that's the hardcoded default.
• With #44 implemented, the tags would be of the form build/<N-E-V-R>, where <N-E-V-R> is the components (name, epoch, version, release) separated by dashes and escaped with rpmautospec.py2compat.tagging.escape_tag() to produce valid git tags (can be unescaped with unescape_tag()).

Acceptance criteria:

• Optionally uses tags for calculating the release number (see above for format).