Allow the PullLocal daemon to actually hibernate

Summary:
Ref T12298. The PullLocal daemon has had hibernation code for a little while, but it never actually activated because we don't sleep for more than 15 seconds in any case.

Add a maximum sleep instead and use that to control the longest sleep we'll do for hibernation purposes.

Also, when a repository or repository URI is edited, write a NEEDS_UPDATE event into the message table to make sure the daemons de-hibernate.

Test Plan: Used bin/phd debug pull, saw the daemon actually hibernate instead of just sleeping for 15 seconds.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12298

Differential Revision: https://secure.phabricator.com/D17635