perf test: Add -F/--dont-fork option

Adding -F/--dont-fork option to bypass forking for each test. It's
useful for debugging test.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Nilay Vaish <nilayvaish@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1467113345-12669-1-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-test.txt

@@ -30,3 +30,7 @@ OPTIONS
 -v::
 --verbose::
 	Be more verbose.
+
+-F::
+--dont-fork::
+	Do not fork child for each test, run all tests within single process.