wikiversions.cdb for labs

This patch adapts multiversion to detect an eventual
wikiversions-labs.cdb file whenever it exists.  With git-deploy we will
have to add the .cdb files to git in order to deploy them, so we want
wikiversions-labs.dat to generate a different cdb file.

Bug: 44424
Change-Id: I812a591225bb7cd9c957cfaa2d3a27f10fd423ee