libperf: Keep count of failed tests

Keep the count of failed tests, so we get better output with failures,
like:

  # make tests
  ...
  running static:
  - running test-cpumap.c...OK
  - running test-threadmap.c...OK
  - running test-evlist.c...FAILED test-evlist.c:53 failed to create evsel2
  FAILED test-evlist.c:163 failed to create evsel2
  FAILED test-evlist.c:287 failed count
    FAILED (3)
  - running test-evsel.c...OK
  running dynamic:
  - running test-cpumap.c...OK
  - running test-threadmap.c...OK
  - running test-evlist.c...FAILED test-evlist.c:53 failed to create evsel2
  FAILED test-evlist.c:163 failed to create evsel2
  FAILED test-evlist.c:287 failed count
    FAILED (3)
  - running test-evsel.c...OK
 ...

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.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/20191017105918.20873-9-jolsa@kernel.org


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