test: Add junit output for unit tests

nosetests allows the generation of junit-like xml files containing the
results. This is useful with jenkins, as jenkins can use these xml files
to monitor trends in unittests.

Change-Id: Ic6d28b83ba309c1973302c48d5658d7bb96fb46f
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>