tests/gem_flink_race: actually make it somewhat useful

- Enable subtest support.

- Add a check for the same flink name in the racing threads, which is
  an issue one of my recent patches actually fixes.

- Add the test I've actually wanted to write which races an flink
  against gem close (with no open in between). That one does indeed
  leak.

- Readd the leak check, but note that this needs a fixed kernel.
  Otherwise the leak counter will be utter garbage.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

tests/Makefile.am

@@ -25,6 +25,7 @@ TESTS_progs_M = \
 	gem_exec_nop \
 	gem_fence_thrash \
 	gem_flink \
+	gem_flink_race \
 	gem_gtt_concurrent_blit \
 	gem_linear_blits \
 	gem_mmap_gtt \
@@ -61,7 +62,6 @@ TESTS_progs = \
 	gem_exec_faulting_reloc \
 	gem_exec_lut_handle \
 	gem_fenced_exec_thrash \
-	gem_flink_race \
 	gem_gtt_cpu_tlb \
 	gem_gtt_speed \
 	gem_hangcheck_forcewake \