Improve /var/lib/fieldworks permission check

* Check VLF, not VLF/SIL/WSS since the latter may not exist,
  resulting in continuing without reporting the problem.
* Check VLF before writing to the registry in case that could
  introduce an unexpected or inconsistent state.
* Give more information to the user:
  * What to do at all, and commands to run.
  * Detect and report if they just need to reboot.
  * Detect and report if they need to recover from poor customization.
* See FWNX-1420.

Change-Id: I34a609e6d2d7f3dc3b395fe19885595d68bb2466