We add a new field domainName to the Kerberos section. The field is used
to setup /etc/idmapd.conf with the domain name. This allows idmapper to
map to kerberos credential to the correct uid/gid.
We add Spec.Security.Kerberos.DomainName to the CRD
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>