Add script to check if build is in compose
    
    The result is indicated in the exit code and a message on stdout (unless
    suppressed with `-q` option). The build can be specified as full NEVR or
    just NVR (in which case we assume epoch 0). It works with local path to
    compose or with a URL to the compose.
    
    Fixes: https://pagure.io/compose-utils/issue/73