Bootstrap MWMultiVersion for default wiki if unset

Make use of MWMultiVersion more user friendly by bootstrapping for use
with the default wiki rather than throwing a fatal error when mwscript
or other initialization is not used.

Bug: 69520
Change-Id: I96dbb3b873b26ef5b2f4a94e4297ca91835837e9
Merge "Bootstrap MWMultiVersion for default wiki if unset"