add apt-cache to the list of things using cnames

Change-Id: Ide7a362bbc619c149e25fae342c71cbe99fa007d
diff --git a/roles/maas/files/update_dns_template.sh b/roles/maas/files/update_dns_template.sh
index 91bc01f..5bb7633 100755
--- a/roles/maas/files/update_dns_template.sh
+++ b/roles/maas/files/update_dns_template.sh
@@ -58,6 +58,7 @@
 \$INCLUDE "/etc/bind/maas/dhcp_harvest.inc"
 $HOSTNAME IN A $LHOST
 docker-registry CNAME $HOSTNAME
+apt-cache CNAME $HOSTNAME
 \$INCLUDE "/etc/bind/maas/cnames.inc"
 {{endif}}
 EOT