Create BINDDNS_DIR/dns.keytab link to PRIVATE_DIR/dns.keytab on DC join
When joining a new Samba DC with the BIND9_BLZ backend the BINDDNS_DIR/dns.keytab link to PRIVATE_DIR/dns.keytab isn't created.
This refactors the link creation code from the samba_upgradedns
script to new method samba.provision.sambadns.create_dns_dir_keytab_link
and call create_dns_dir_keytab_link
after create_dns_dir
.
I don't see any existing tests for samba.provision.sambadns
to modify.