pytest: Use the same TIMEOUT in wait_for_route

This was getting flaky whenever we had multihop routing syncs and had
`DEVELOPER=0`, which uses the slow gossip propagation.

contrib/pyln-testing/pyln/testing/utils.py

@@ -961,7 +961,7 @@ def wait_for_channel_updates(self, scids):
                                   + ['Received channel_update for channel {}/1'.format(c)
                                      for c in scids])
 
-    def wait_for_route(self, destination, timeout=30):
+    def wait_for_route(self, destination, timeout=TIMEOUT):
         """ Wait for a route to the destination to become available.
         """
         start_time = time.time()