Set bind propagation mode for media (#4308)

* Set bind propagation mode for media

* Add some test cases

tests/docker/test_observer.py

@@ -0,0 +1,38 @@
+"""Test Observer plugin container."""
+
+from ipaddress import IPv4Address, ip_network
+from unittest.mock import patch
+
+from docker.types import Mount
+
+from supervisor.coresys import CoreSys
+from supervisor.docker.manager import DockerAPI
+
+
+async def test_start(coresys: CoreSys):
+    """Test starting observer plugin."""
+    with patch.object(DockerAPI, "run") as run:
+        await coresys.plugins.observer.start()
+
+        run.assert_called_once()
+        assert run.call_args.kwargs["ipv4"] == IPv4Address("172.30.32.6")
+        assert run.call_args.kwargs["name"] == "hassio_observer"
+        assert run.call_args.kwargs["hostname"] == "hassio-observer"
+        assert run.call_args.kwargs["restart_policy"] == {"Name": "always"}
+        assert run.call_args.kwargs["extra_hosts"] == {
+            "supervisor": IPv4Address("172.30.32.2")
+        }
+        assert run.call_args.kwargs["oom_score_adj"] == -300
+        assert run.call_args.kwargs["environment"]["NETWORK_MASK"] == ip_network(
+            "172.30.32.0/23"
+        )
+        assert run.call_args.kwargs["ports"] == {"80/tcp": 4357}
+        assert run.call_args.kwargs["mounts"] == [
+            Mount(
+                type="bind",
+                source="/run/docker.sock",
+                target="/run/docker.sock",
+                read_only=True,
+            ),
+        ]
+        assert "volumes" not in run.call_args.kwargs