Labs: manage resolv.conf in labs also

Labs currently uses the install-default resolv.conf rather
than manage it with puppet. This corrects that, and adds
a template for it with suitable values for labs.

There are two FIXMEs this will need: put the template
outside of modules/base (requires making a module for labs)
and find a clean way to bubble down the nameserver IP rather
than hardcode it (it's currently hardcoded in a half-dozen
places).

Bug: T63897
Change-Id: I290c32fdeedc9319b804f886c21fe1c49a6c864f