Code review comment for ~canonical-kernel-team/+git/autotest-client-tests:phlin/ftrace-granularity

I have this patch tested on node janbi with j-realtime, with 10 minute timeout and 30 minute timeout.

The results are identical:
* 10 min
  - timeout ubuntu_kselftests_ftrace.ftrace:test.d--direct--ftrace-direct.tc
  - timeout ubuntu_kselftests_ftrace.ftrace:test.d--event--subsystem-enable.tc
  - fail ubuntu_kselftests_ftrace.ftrace:test.d--ftrace--func_traceonoff_triggers.tc
* 30 min
  - timeout ubuntu_kselftests_ftrace.ftrace:test.d--direct--ftrace-direct.tc
  - timeout ubuntu_kselftests_ftrace.ftrace:test.d--event--subsystem-enable.tc
  - fail ubuntu_kselftests_ftrace.ftrace:test.d--ftrace--func_traceonoff_triggers.tc

They all timeout / fail on the same point, please find the log here:
https://bugs.launchpad.net/ubuntu-kernel-tests/+bug/2027770/comments/1
https://bugs.launchpad.net/ubuntu-kernel-tests/+bug/2027770/comments/2

Therefore I think we can keep the timeout as 10min.