test: systemctl stop user@ now drops the root session

With systemd 256-rc1 systemctl stop user@* also stops user@0 the root
user's service so kills the open ssh connection making `m.execute` fail.

Combine stopping the user service with the loginctl cleanup.

test/common/testlib.py

@@ -1688,18 +1688,18 @@ def terminate_sessions() -> None:
             self.machine.execute("systemctl stop systemd-logind")
 
             # Wait for sessions to be gone
-            sessions = self.machine.execute("loginctl --no-legend list-sessions | awk '/web console/ { print $1 }'").strip().split()
-            for s in sessions:
+            sessions = self.machine.execute("loginctl --no-legend list-sessions | awk '/web console/ { print $1,$2 }'").strip().split()
+            for session in sessions:
+                sessionid, uid = session.split(',')
                 try:
-                    m.execute(f"while loginctl show-session {s}; do sleep 0.2; done", timeout=30)
+                    m.execute(f"while loginctl show-session {sessionid}; do sleep 0.2; done", timeout=30)
+                    # Terminate systemd user service
+                    m.execute(f"systemctl stop user@{uid}.service")
                 except RuntimeError:
                     # show the status in debug logs, to see what's wrong
-                    m.execute(f"loginctl session-status {s}; systemd-cgls", stdout=None)
+                    m.execute(f"loginctl session-status {sessionid}; systemd-cgls", stdout=None)
                     raise
 
-            # terminate all systemd user services for users who are not logged in
-            self.machine.execute("systemctl stop user@*.service")
-
             # Clean up "closing" sessions again, and clean user id cache for non-system users
             self.machine.execute("systemctl stop systemd-logind; cd /run/systemd/users/; "
                                  "for f in $(ls); do [ $f -le 500 ] || rm $f; done")