[OXT-24] Add local.conf-dist from xenclient-oe.git.

This is the default / template local.conf file that we've used
historically.
[OXT-24] Treat the xenclient-oe.git repo like it was any other meta layer.

We clone it using the same mechanism we use for the other meta layers
and we clone it in the same location. Also I've started calling it
'meta-openxt' where possible. The remote still needs to be renamed
but it's not worthy of the name yet :)