weldr-client has replaced composer-cli so remove all of the code and
tests, adjust various things so they don't expect it to be available,
and rename some things like test/composertest.py to reflect its
exclusive use by lorax.
(cherry picked from commit b75b692607)
These use beakerlib to download a Fedora boot.iso and run mkksiso on
it. It currently does not try to boot the resulting iso, it mounts it
and checks that the expected config files have been modified and the
extra files have been added.