perf tests: Let 'perf test list' display subtests

perf tests: Let 'perf test list' display subtests

The output of perf test and perf test list differ because perf test list
does not display subtests.  Correct this behavior and also let perf test
list report subtests.

For example:

	$ ./perf test 2>&1 |wc -l
	65

Without this commit:
	$ ./perf test list 2>&1 |wc -l
	57

With this commit:
	$ ./perf test list 2>&1 |wc -l
	65

Signed-off-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Reviewed-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: linux-s390@vger.kernel.org
LPU-Reference: 1523605343-11970-1-git-send-email-brueckner@linux.ibm.com
Link: https://lkml.kernel.org/n/tip-efb74jw7x2xs2bucp5hf4ilu@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>