Add a negative test to test__checkevent_pmu_events() to get lots of
coverage of the negative case, ie. when the modifier is not specified.

Add a test of a single event, and of the group case.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1375795686-4226-2-git-send-email-michael@ellerman.id.auSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>