Call Build::LiveBuild::parse for file matching *.live-build.tar

Signed-off-by: Jan Blunck <jblunck@vyatta.com>
Let expanddeps return live-build dependencies

When expanddeps finds a live-build configuration tarball it should return
the dependencies of live-build instead of parsing the configuration itself
(which is created by another service and is handed to build).

Signed-off-by: Jan Blunck <jblunck@vyatta.com>
Make build accept *.live-build.tar "SPECFILES"

Signed-off-by: Jan Blunck <jblunck@vyatta.com>