systrace: fix tracefs device path detection
systrace: fix tracefs device path detection

There are devices which has debugfs mounted but trace path is moved.
Fix this by selecting trace path based on tracefs path existence.

Test: systrace
Signed-off-by: Wei Wang <ae8a4d7d04957c52407ebbfaaa676fc6453e5f97@google.com>
Change-Id: I720c35a04b950b4926e6fcd4dbd3ab2db368dd93
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/2826726
Commit-Queue: Hridya Valsaraju <95e1b8401f8dc7393e63c1a41e0380b2c85844d2@google.com>
Reviewed-by: Chris Craik <24a70e8781b9b8b74f2d02f7b3f73348969c172b@google.com>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult