Make scap restart HHVM

If we keep syncing new code without restarting HHVM, HHVM's JIT and PCRE caches
will eventually run out of space, leading HHVM to skip certain optimizations
and eventually crash. To mitigate that, restart the HHVM service when scap is
done. Depends on change I60115d46a in operations/puppet.

Change-Id: Idc01b17ca52922cc71c5e04260c3c098317f6496