Skip LuaWikibaseLibraryTest if repo not present

Scribunto_LuaWikibaseLibraryTest needs to access the repo
database, which it can't if the client is running stand-alone.

Change-Id: Ife4a95f85504777db5cf195f07aa541d394a664a
Merge "Skip LuaWikibaseLibraryTest if repo not present"