base: Factor out SSH host, user cert roles

Moving the SSH host and user certificate configuration roles out of
`base.yml` into their own playbooks.  This will make it easier to deploy
them separately, and target different sets of hosts.  The main driver
for this change is the OVH VPS; being external, it cannot communicate
with SSHCA and thus cannot have a signed host certificate.  As such, we
do not want to try to configure the SSHCA client on it at all.

base.yml

@@ -2,9 +2,6 @@
 - hosts: all
   roles:
   - base
-  - role: ssh-host-certs
-    tags: ssh-host-certs
-  - ssh-user-ca
 - hosts: kvm-guest
   roles:
   - serial-console

bootstrap.yml

@@ -2,3 +2,5 @@
 - import_playbook: hostname.yml
 - import_playbook: base.yml
 - import_playbook: firewalld.yml
+- import_playbook: ssh-host-certs.yml
+- import_playbook: ssh-user-ca.yml

ssh-host-certs.yml

@@ -0,0 +1,4 @@
+- hosts: '!vps'
+  roles:
+  - role: ssh-host-certs
+    tags: ssh-host-certs

ssh-user-ca.yml

@@ -0,0 +1,3 @@
+- hosts: all
+  roles:
+  - ssh-user-ca