Add _get_module in DBResolver and fix _record_ursine_rpms
    
    _record_ursine_rpms needs to get each collision module's koji_tag and
    then get built RPMs from that koji_tag eventually. _get_module on each
    individual resolver is called to get module metadata accordingly. So,
    when running a local build, module metadata is got from remote MBS, and
    for a MBS instance, connected database is queried.
    
    Signed-off-by: Chenxiong Qi <cqi@redhat.com>