[fallback] Make the get_stats timeout configurable and default to 5m

Go test seems to fail because timeout is too short. Making it
configurable should help with the debugging. Also, setting it
to 5m may just fix the issue.

framework/helpers/docker.py

@@ -260,6 +260,7 @@ def __init__(
         name: str,
         url: str,
         image: str,
+        stats_request_timeout_s: str,
     ):
         super().__init__(
             manager=manager,
@@ -278,13 +279,14 @@ def __init__(
                 }
             },
         )
+        self.stats_request_timeout_s = stats_request_timeout_s
 
     def get_stats(self, num_rpcs: int):
         logger.debug("Sending %d requests", num_rpcs)
         stub = test_pb2_grpc.LoadBalancerStatsServiceStub(self.channel())
         res = stub.GetClientStats(
             messages_pb2.LoadBalancerStatsRequest(
-                num_rpcs=num_rpcs, timeout_sec=math.ceil(num_rpcs * 10)
+                num_rpcs=num_rpcs, timeout_sec=self.stats_request_timeout_s
             )
         )
         return res

tests/fallback_test.py

@@ -49,7 +49,11 @@
 _STATUS_POLL_INTERVAL_MS = flags.DEFINE_integer(
     "status_poll_interval_ms", 300, "Channel status poll interval (in ms)"
 )
-
+_STATS_REQUEST_TIMEOUT_S = flags.DEFINE_integer(
+    "stats_request_timeout_s",
+    300,
+    "Number of seconds the client will wait for the requested number of RPCs",
+)
 _LISTENER = "listener_0"
 
 absl.flags.adopt_module_key_flags(framework.xds_k8s_testcase)
@@ -92,6 +96,7 @@ def start_client(self, port: int = None, name: str = None):
             port=port or get_free_port(),
             url=f"xds:///{_LISTENER}",
             image=framework.xds_k8s_flags.CLIENT_IMAGE.value,
+            stats_request_timeout_s = _STATS_REQUEST_TIMEOUT_S.value,
         )
 
     def start_control_plane(