[live-media] Use subvariants in logging
Print the subvariant together with variant UID and arches. This should
make the global log easier to understand.
The output of koji command should now be split into multiple files in
logs/{arch}/livemedia-{variant}-{subvariant}.{arch}.log instead of
having them all in one file.
The tests were updated to use more sensible value for the subvariant
field.
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>