Stop using process/filesystem-based checks to determine if daemons are running

Summary:
We currently check if daemons are running using the filesystem and process list. These checks reach the wrong result for a lot of users because their webservers can't read the filesystem or process list. They also reach the wrong result for daemons running on other machines.

Instead, query the active daemon list to see if daemons are running. This should be significantly more reliable.

(We didn't do this before because the running daemon list mechanism didn't exist when the check was written, and at the time it was more complex than doing a simple filesystem/process list thing.)

Test Plan: Viewed /repositories/ with and without daemons running, saw appropriate warning or lack of warning.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6722