Update hhvm config

* Bring closer to mediawiki vagrant
** Moved most settings to php.ini
** Updated dynamic extension path
** But the admin console etc. were not added
* Use unix socket
* Disable hhvm fastcgi by default still

Change-Id: I9da2a1c359835df9fe246faf2f6d067a7f1e0ed7
Merge "Update hhvm config"