Qfs kerberos lib: fix KrbClient ticket cache initialization to work with older kerberos 5 revisions, that have no krb5_get_init_creds_opt_set_out_ccache() by explicitly [re] initializing the ticket cache with the client principal obtained from the key tab and then storing credentials. Fix unit test to properly handle the command line arguments, add more verbose "usage" display, add "M" flag to allow to disable the "MEMORY:" keytab to make the test work with older kerberos revisions that have no "MEMORY" key tab support.