systemd: Escape only needed characters for machined
    
    Machine name escaping follows the same rules as serice name escape,
    except that '.' and '-' must not be escaped in machine names, due
    to a bug in systemd-machined.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1282846
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>