Add support for username and password based authentication for pagure-ci
    
    We used to query jenkins directly via an username provided URL, we
    switch to using the python jenkins library, which requires username and
    password to be specified in a different way.
    This commit asks for the user to specify the username and password to
    use to authenticate to jenkins and provides them to the python jenkins
    library as they should be.
    
    Fixes https://pagure.io/pagure/issue/4120
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>