use available api to check daemon status

Summary:
Replace executing 'ps aux' with usage of available api to
control daemons PhabricatorDaemonControl.

This fixes isPullDaemonRunningOnThisMachine returning wrong status
under Fedora & lighttpd & SELinux because SELinux with default
settings blocked getting all processes in 'ps aux'.

Test Plan: start stop daemon and check repository app

Reviewers: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3557