perf tests: Add daemon 'stop' command test

Add a test for the perf daemon 'stop' command. The test stops the daemon
and verifies all the configured sessions are properly terminated.

Committer testing:

  [root@five ~]# time perf test daemon
  76: daemon operations                                               : Ok
  [root@five ~]# time perf test -v daemon
  76: daemon operations                                               :
  --- start ---
  test child forked, pid 788560
  test daemon list
  test daemon reconfig
  test daemon stop
  test child finished with 0
  ---- end ----
  daemon operations: 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: Alexei Budankov <abudankov@huawei.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: https://lore.kernel.org/r/20210208200908.1019149-22-jolsa@kernel.org


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