nova-libvirt: conditionalize selinux bind-mount

on a F28-based container image nova-libvirt fails to
start in Podman if /sys/fs/selinux is bind-mounted
from the host, with the following logs:

2019-01-16 13:41:35.375+0000: 452430: error : virSecuritySELinuxQEMUInitialize:634 : cannot open SELinux label_handle: No such file or directory
2019-01-16 13:41:35.375+0000: 452430: error : qemuSecurityInit:425 : internal error: Failed to initialize security drivers
2019-01-16 13:41:35.375+0000: 452430: error : virStateInitialize:775 : Initialization of QEMU state driver failed: internal error: Failed to initialize security drivers
2019-01-16 13:41:35.375+0000: 452430: error : daemonRunStateInit:837 : Driver state initialization failed

Perform the bind-mount only when the ContainerCli is set
to 'docker'.

Change-Id: I7a2ca4fb1ff8ea5950fd52774c648af5ef274796
Closes-Bug: #1812013
Co-Authored-By: Michele Baldessari <michele@acksyn.org>

docker/services/nova-libvirt.yaml

@@ -134,6 +134,13 @@ parameters:
     tags:
       - role_specific
 
+  ContainerCli:
+    type: string
+    default: 'docker'
+    description: CLI tool used to manage containers.
+    constraints:
+      - allowed_values: ['docker', 'podman']
+
 conditions:
 
   use_tls_for_live_migration:
@@ -179,6 +186,11 @@ conditions:
       - {get_param: QemuMemoryBackingDir}
       - ''
 
+  docker_enabled:
+    equals:
+      - {get_param: ContainerCli}
+      - 'docker'
+
 resources:
   RoleParametersValue:
     type: OS::Heat::Value
@@ -345,7 +357,12 @@ outputs:
                   - /var/log/containers/libvirt:/var/log/libvirt:z
                   - /var/log/libvirt/qemu:/var/log/libvirt/qemu:ro
                   - /var/lib/vhost_sockets:/var/lib/vhost_sockets:z
-                  - /sys/fs/selinux:/sys/fs/selinux
+                -
+                  if:
+                    - docker_enabled
+                    -
+                      - /sys/fs/selinux:/sys/fs/selinux
+                    - null
                 -
                   if:
                     - use_tls_for_live_migration