tripleo-podman: Enable and start podman.socket

It might be a good idea to control wether or not the podman.socket
service is enabled in case we want to podman --remote.

We plan on using this in the wrapper services instead of relying on
nsenter.

Cherry-pick included in this patch.
* https://review.opendev.org/c/openstack/tripleo-ansible/+/817202

Changes which are already cherry-picked:
* https://review.opendev.org/q/Ifca971e14abb184c4b7b8a0d004e8c2fbd0ecb68
* https://review.opendev.org/q/Iefe861f91cefe2a9cf773cae98b2440566ae8b5e
* https://review.opendev.org/q/Ibdf87463d4a86dd225a1f1b89326407628facb65

Change-Id: I52d63d34a9c01bac7e77f2ce9154aa719b4f82b5
(cherry picked from commit 7f5ecb62b5)

releasenotes/notes/tripleo-podman-enable_socket-f93bdaa47f4b01d9.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    tripleo-podman now has the ability to enable podman.socket service when
+    tripleo_podman_enable_socket is enabled.

tripleo_ansible/roles/tripleo_podman/defaults/main.yml

@@ -27,6 +27,7 @@ tripleo_podman_packages: "{{ _tripleo_podman_packages | default([]) }}"
 tripleo_buildah_packages: "{{ _tripleo_buildah_packages | default([]) }}"
 tripleo_podman_purge_packages: "{{ _tripleo_podman_purge_packages | default([]) }}"
 tripleo_podman_tls_verify: true
+tripleo_podman_enable_socket: false
 tripleo_podman_unqualified_search_registries:
   - registry.redhat.io
   - registry.access.redhat.com
@@ -79,3 +80,4 @@ tripleo_podman_registries: []
 tripleo_container_default_pids_limit: 4096
 tripleo_container_events_logger_mechanism: journald
 tripleo_container_default_runtime: runc
+tripleo_container_default_infra_image: "registry.access.redhat.com/ubi8/pause"

tripleo_ansible/roles/tripleo_podman/tasks/tripleo_podman_install.yml

@@ -94,3 +94,14 @@
         - section: engine
           option: runtime
           value:  "\"{{ tripleo_container_default_runtime }}\""
+        - section: engine
+          option: infra_image
+          value:  "\"{{ tripleo_container_default_infra_image }}\""
+
+    - name: Enable podman.socket service
+      when:
+        - tripleo_podman_enable_socket | bool
+      systemd:
+        name: podman.socket
+        state: started
+        enabled: true