perf tests: Consider subtests when searching for user specified tests

It's now possible to put subtest name as a test filter:

  $ perf test 'PMU event table sanity'
  10: PMU events                                            :
  10.1: PMU event table sanity                              : Ok

Committer testing:

Before:

  $ perf test 'PMU event table sanity'
  $

After:

  $ perf test 'PMU event table sanity'
  10: PMU events                                            :
  10.1: PMU event table sanity                              : Ok
  $

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200524224219.234847-2-jolsa@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>