beta: prep for rc 1.3, fix compose tag, fix image label
    
    Prep for doing a 1.3 compose (1.1 and 1.2 were not usable)
    
    Fix the compose tag to use f38-compose, so we pick up the builds that
    are overrides from the nightly/regular composes.
    
    Fix the image label to include Beta in it instead of being date based
    like the nightly ones.
    
    Signed-off-by: Kevin Fenzi <kevin@scrye.com>