krb5: Fetch ccname template from krb5.conf
    
    In order to use the same defaults in all system daemons that needs to know how
    to generate or search for ccaches we introduce ode here to take advantage of
    the new option called default_ccache_name provided by libkrb5.
    
    If set this variable we establish the same default for all programs that surce
    it out of krb5.conf therefore providing a consistent experience across the
    system.
    
    Related:
    https://fedorahosted.org/sssd/ticket/2036