ipaclient: Fix allow_repair with removed krb5.conf and DNS lookup

The test in ipaclient_test_keytab is at first trying to use an existing
krb5.conf to test if the host keytab can be used. With working DNS lookup
an absent krb5.conf is not reported as an error as DNS lookup is
silently used instead.

A temporary krb5.conf is now used in this test that forces to deactivate
DNS lookups and also to load /etc/krb5.conf. A missing krb5.conf is now
detected properly as the kinit call fails now properly. Thanks to Julien
Rische for this proposal.

ipaclient_test_keytab is now properly returning the state of usable or
not usable krb5.conf in krb5_conf_ok. This fixes the handling of this
case later on in the role.