trivial: installed-tests: skip tests requiring network by default
trivial: installed-tests: skip tests requiring network by default

Most of the installed tests will skip if files needed to be fetched
from network are not available.  Do the same thing for fwupdmgr
tests.

Fixes: #2566

hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd