Auto acquire Kerberos credential
    
    Two ways to acquire credential automatically. For running freshmaker in
    a server, client keytab is used to acquire and store ticket in a
    specified ccache. For running in local development, especially for
    making a demo, kinit with personal user principal is required. In both
    of these cases, ccache can be re-initialized again with new ticket when
    old one expires.
    
    Signed-off-by: Chenxiong Qi <cqi@redhat.com>