qa: improve and add commit ID to comment for context

The comment was unclear without looking at previous version of code.
Therefore improve comment a bit and add link to commit ID due to which
this comment was introduced to give future readers context.

Also, place the comment before the command arguments. This too adds the
context.

Signed-off-by: Rishabh Dave <[email protected]>

Author: rishabh-d-dave

qa/tasks/workunit.py

@@ -441,8 +441,10 @@ def _run_tests(ctx, refspec, role, tests, env, basedir,
                     remote.run(logger=log.getChild(role), args=args, timeout=(60*60))
     finally:
         log.info('Stopping %s on %s...', tests, role)
+        # N.B. unlike before, don't cleanup path under variable "scratch_tmp"
+        # here! If the mount is broken then rm will hang. For context, see
+        # commit d4b8f94cf8d95ebb277b550fc6ebc3468052a39c.
         args=['sudo', 'rm', '-rf', '--', workunits_file, clonedir]
-        # N.B. don't cleanup scratch_tmp! If the mount is broken then rm will hang.
         remote.run(
             logger=log.getChild(role),
             args=args,