forgetest: a takeover waits for forgectrl to settle on both sides

forgectrl's supervisor probes motion liveness on every start - a small
head move verified by the accelerometer, with a rail-off ladder of up to
about 70 s on a dead verdict. The takeover wrapper returned as soon as
forgectrl start succeeded, so a test that followed found the machine
busy (bench: cooling.flow-verify refused with 409 machine is not idle
13 s after kernel.fire-abu), and back-to-back takeover tests stopped
forgectrl mid-probe. The wrapper now waits for /mode to settle - motion
verified, motion-fault (logged as a warning), or standby - before it
stops forgectrl and again after it starts it, giving up after 10 s when
forgectrl does not answer at all (the host, or a daemon that is down).
No catalog consequence: the takeover tests' own drills are unchanged.

forgetest/tests/test_server.py

@@ -287,10 +287,11 @@ class ServerTests(unittest.TestCase):
         # a takeover tool runs inside the takeover wrapper (init.d is absent on the host: rc 127)
         st, d = self.call("POST", "/bench/start", {"tool": "tk"})
         self.assertEqual(st, 200, d)
-        state = self.wait_idle()
+        state = self.wait_idle(timeout=40)     # two unreachable-forgectrl settle waits
         log = "\n".join(state["last_run"]["log"])
         self.assertIn("takeover: pulse device free", log)
         self.assertIn("takeover: forgectrl start", log)
+        self.assertIn("takeover: forgectrl unreachable for 10 s", log)
         self.assertFalse(os.path.exists(os.environ["FORGETEST_MARKER"]))
         # bench runs never touched the acceptance log
         recs = self.log.read()