machine_core: Check for cockpit.socket instead of OSTree for starting…

… Cockpit

We want to test the cockpit/ws container with beibooting on other images
than just OSTree. So for deciding whether to start the systemd unit or
the container, check if the unit exists, instead of hardcoding "exactly
OStree uses ws".

Tests currently check the `Machine.ostree_image` flag both for *actual*
specifics of OSTree (such as a read-only /usr) as well as a proxy for
"am I running Cockpit from the container". As this won't coincide in the
future, introduce a new `Machine.ws_container` flag.

machine/machine_core/machine.py

@@ -251,7 +251,11 @@ def start_cockpit(self, *, tls: bool = False) -> None:
         allow you to make modifications before it starts.
         """
 
-        if self.ostree_image:
+        # start via cockpit/ws container if cockpit-ws package isn't installed
+        self.ws_container = not self.execute("systemctl --no-legend list-unit-files cockpit.socket",
+                                             check=False).strip()
+
+        if self.ws_container:
             self.stop_cockpit()
             cmd = "podman container runlabel RUN cockpit/ws"
             if not tls:
@@ -284,7 +288,7 @@ def start_cockpit(self, *, tls: bool = False) -> None:
     def restart_cockpit(self) -> None:
         """Restart Cockpit.
         """
-        if self.ostree_image:
+        if self.ws_container:
             self.execute(f"podman restart {self.get_cockpit_container()}")
             self.wait_for_cockpit_running()
         else:
@@ -293,7 +297,7 @@ def restart_cockpit(self) -> None:
     def stop_cockpit(self) -> None:
         """Stop Cockpit.
         """
-        if self.ostree_image:
+        if self.ws_container:
             self.execute(f"echo {self.get_cockpit_container()} | xargs --no-run-if-empty podman rm -f")
         else:
             self.execute("systemctl stop cockpit.socket cockpit.service")