NOTE that the tests against the rpmmd fixure for running and waiting are
a bit of a kludge. It is impossible to mock up a running or waiting that
will allow an actual cancel, so the tests check for the internal server
error generated by using the fixure data.
Getting this error means that the API code did it's job and tried to
cancel the compose so that should be a good compromise.
Also adds new types to weldr/json.go to support them.
ComposeEntry had to be duplicated instead of used as-is because it
enforces image type strings that do not match what the API uses (the API
types are all lower case, the internal names are capitalized).
