buildstats: Drop get_bn/set_pn and just use BUILDNAME
The current setting and getting of the "name" to use for buildstats is
convoluted and not particularly interesting. We only need this for the
e.getPkgs()[0] component of the path which is the first target listed
on the commandline. This is pretty arbitrary.
If we drop that piece, we can assume BUILDNAME is common for all events
and simply use this and query it. If BUILDNAME did change, that would
be a bug and it should be fixed elsewhere.
Also take the opportunity to share some common code since the function
now has the eventmask.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
