Allow wikidev users to restart HHVM

* Remove sudo privs for restrating nutcracker for wikidevs. This is carry-over
  from the time when we managed the Nutcracker configs in wmf-config.
  Nutcracker config changes require a root to merge now.
* Allow wikidevs to restart HHVM, so it can be done automatically as part of
  scap. Otherwise, the trace cache and PCRE cache will eventually run out of
  space and HHVM will either skip certain optimizations or crash.

Change-Id: I60115d46aa9329966908a9216361e45acdedf4bd