zdtm: print a summary of failed tests if using --keep-going

When using the option --keep-going to get a quick overview of the test
results there is now a summary which tests have failed like:

 ############# 7 TEST(S) FAILED (TOTAL 268/SKIPPED 83) ##############
  * zdtm/static/sched_policy00(unknown)
  * zdtm/static/pthread00(unknown)
  * zdtm/static/pthread01(unknown)
  * zdtm/static/maps01(unknown)
  * zdtm/static/maps00(unknown)
  * zdtm/transition/maps008(unknown)
  * zdtm/transition/shmem(unknown)
 ############################### FAIL ###############################

Signed-off-by: Adrian Reber <areber@redhat.com>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>