tools/lib/lockdep/tests: Improve testing accuracy

tools/lib/lockdep/tests: Improve testing accuracy

Instead of checking whether the tests produced any output, check the
output itself. This patch avoids that e.g. debug output causes the
message "PASSED!" to be reported for failed tests.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: johannes.berg@intel.com
Cc: tj@kernel.org
Link: https://lkml.kernel.org/r/20181207011148.251812-4-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>