Get the NSVC from Koji module CG build metadata
    
    Stream can contain dash sign and when MBS imports such NSVC to Koji, the
    dash is replaced with underscore. The current Pungi code does not
    respect that and tries to use the stream from Koji directly, which
    results in wrong stream being using in some Pungi internal data.
    
    In this PR, the NSVC is taken from module metadata section of CG Koji
    build, which contains real stream including the dashes.
    
    Merges: https://pagure.io/pungi/pull-request/1072
    Signed-off-by: Jan Kaluza <jkaluza@redhat.com>