Minion env matching extended with taskotron_match_* vars
    
    Playbooks can now contain these variables for to specify required
    environment:
    - taskotron_match_host_distro
    - taskotron_match_host_release
    - taskotron_match_host_arch
    
    If not present, values default to False and default values from
    config file are used instead.
    
    This restructures how variables are loaded and process into hopefully a
    clearer process. Heavily adjusted by kparal and jskladan, so those are
    to blame as well.
    
    Merges https://pagure.io/taskotron/libtaskotron/pull-request/413