Vastly increase how long wfWaitForSlaves() can block in CLI mode

* All maintenance scripts pretty much assumed this behavior, but it
  was not actually the case. This can avoid some massive lag problems.

Change-Id: I5894409d6abade16afd8144f6689c2aff3fa7327
(cherry picked from commit cafcb6b2258a10746409135037baa9ac4ab6089e)