koji now supports tags with max length of 256, we can use
more informative tag name instead of the hash one.
The new format of koji tag name is:
module-<name>-<stream>-<version>-<context>
However when the generated tag's length > (256 - len('build')), we
fallback to the old way of name in hash format (module-<hash>).
In this change, koji tag is always generated from MBS itself, even
with pdc resolver.
FIXES: #918#925