perf tests: Add return states enum for tests

Test can currently return one of 3 states: ok, fail, skip.

The ok and fail states are self-explanatory. The skip state means that
some of the conditions for running the test was not met, making it
impossible to even run the test. For instance, if the hardware doesn't
support the 'precise' level required by a test, it will be skipped.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lkml.kernel.org/n/tip-04vnsdndarctfb1eii5c9hcy@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>