Don't disable Wikibase or LuaSandbox when running under HHVM

I disabled Wikibase for HHVM on Labs due to bug 63691. This patch keeps it
disabled in Labs but enables it for osmium, so we can see if it's still an
issue.

LuaSandbox was not enabled under HHVM because it was not available. It is now.

Change-Id: I093bb98ea18b3c35f99a6bdf384aaf83a2ad5a94