Allow NetworkManager to work (if present)

This patch adds tasks that check to see if NetworkManager is
installed and running. If it is, the tasks allow NetworkManager
to handle the `lxcbr0` interface.

In addition, the `NetworkManager-wait-online.service` will be
enabled to ensure that all services that depend on networking will
wait for network configuration to be completed.

Partial-Bug: 1738467
Change-Id: I415241daccf22f03826062eea18b3b36b2d9e53e

releasenotes/notes/networkmanager-compatibility-87c7c1c121469714.yaml

@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    The ``lxcbr0`` bridge now allows NetworkManager to control it, which
+    allows for networks to start in the correct order when the system boots.
+    In addition, the ``NetworkManager-wait-online.service`` is enabled to
+    ensure that all services that require networking to function, such as
+    ``keepalived``, will only start when network configuration is complete.
+    These changes are only applied if a deployer is actively using
+    NetworkManager in their environment.

tasks/lxc_net.yml

@@ -13,6 +13,24 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# NOTE(mhayden): One of three exit codes should be returned.
+#   0 = service is running
+#   3 = service is installed, but not running
+#   4 = service is not installed, and not running
+- name: Check if NetworkManager is running
+  command: systemctl status NetworkManager
+  changed_when: false
+  failed_when: false
+  register: networkmanager_check
+  tags:
+    - skip_ansible_lint
+
+- name: Ensure network services wait on networking (if using NetworkManager)
+  service:
+    name: NetworkManager-wait-online.service
+    status: enabled
+  when: networkmanager_check.rc == 0
+
 - name: Drop lxc net bridge
   template:
     src: "{{ item.src }}"

templates/lxc-net-redhat-bridge.cfg.j2

@@ -9,6 +9,6 @@ GATEWAY={{ lxc_net_gateway }}
 {% endif %}
 ONBOOT=yes
 BOOTPROTO=none
-NM_CONTROLLED=no
+NM_CONTROLLED={{ (networkmanager_check.rc == 0) | ternary('yes', 'no') }}
 DELAY=0
 STP=no