Fix HHVM restarting routines

Tags: Release-Engineering-Team

Maniphest Tasks: T104352, T146656

Summary:
Fix the cli tool, also unbreak sync and hhvm-graceful

Subject: The cli tool is now supporting both upstart and systemd-based
distros. Commands "sync" and "hhvm-graceful" both try to use an
inexistent task "restart_hhvm", and implementing it is not exactly
an easy task. Raise and manage a NotImplementedError while
we have no implementation for it.

Reviewers: fgiunchedi, thcipriani, Release-Engineering-Team, O2 Release & Deployment Tools, mmodell

Reviewed By: thcipriani, Release-Engineering-Team, O2 Release & Deployment Tools, mmodell

Subscribers: jenkins, Joe

Differential Revision: https://phabricator.wikimedia.org/D411