Declare 2 variables to be global to avoid reference error

This fixes a bug introduced in Ic7fc3bd8362 resulting in the updater
aborting when attempting to update the constraints with a fatal error
due to missing $wgDBname, $wgDBmwschema in the current scope.

Change-Id: I7bbaef2175f81ab843ad09fe92c10dba1257a184