packet: disable syncing allowed SSH keys on nodes

This commit disables syncing authorized SSH keys for core user on nodes
from Packet's user's keys and project's keys, so only keys which are
specified in the Lokomotive configuration are actually authorized, as
having more keys allowed than specified in the configuration might be a
potential security threat.

Closes #465

Signed-off-by: Mateusz Gozdek <mateusz@kinvolk.io>

assets/lokomotive-kubernetes/packet/flatcar-linux/kubernetes/cl/controller.yaml.tmpl

@@ -34,6 +34,8 @@ systemd:
       enable: true
     - name: locksmithd.service
       mask: true
+    - name: coreos-metadata-sshkeys@core.service
+      mask: true
     - name: wait-for-dns.service
       enable: true
       contents: |

assets/lokomotive-kubernetes/packet/flatcar-linux/kubernetes/workers/cl/worker.yaml.tmpl

@@ -19,6 +19,8 @@ systemd:
       enable: true
     - name: locksmithd.service
       mask: true
+    - name: coreos-metadata-sshkeys@core.service
+      mask: true
     - name: wait-for-dns.service
       enable: true
       contents: |