ci: Use SSH host keys from ssh-hostkeys role

I don't know why I didn't think of this before!  There's no reason to
have to have already copied the `ssh_known_hosts` file from to
`/etc/ssh` before running `ansible-playbook`.  In fact, keys just end up
getting copied from `/etc/ssh/ssh_known_hosts` into `~/.ssh/known_hosts`
anyway.  So let's just make it so that step isn't necessary: copy the
host key database directly to `~/.ssh` and avoid the trouble.

vars/applyConfigPolicy.groovy

@@ -54,6 +54,8 @@ def stageKinit() {
             sh 'cp "${SUDO_PASS_FILE}" group_vars/pyrocufflink/sudo-pass'
         }
         sh 'rm -rf .fact-cache'
+        sh 'install -m u=rwx,go= -d ~/.ssh'
+        sh 'cp roles/ssh-hostkeys/files/ssh_known_hosts ~/.ssh/known_hosts'
     }
 }