debian: Update control file for kerberos support

Recommend heimdal-clients and kstart debian packages since they
are needed for nsupdate to authenticate using the kerberos method.

Recommend bind9utils debian package that ships dnssec-keygen
which is needed to create the key pair needed for the bind9
authentication method.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>