Add a new command line option `--skip-tag` that will skip tagging
after a successful build. The help text is copied from the same
option of other sub-commands in the koji client. The hub plugin's
jsonschema was updated accordingly, and the builder plugin will
skip the tag if the option was requested.
Tests were added or augmented for all three plugins to test the
new option.
Currently we were passing the repo information as a comma
separated string, which is fragile, since urls can contain
commas. Just transfer them as arrays of strings.
When waiting for the task, return the result from the `watch_task`
call, which will indicate if the task was successful. This will
then be reflected in the error code of the koji call.
