Make test_idf_isolated_withdraw_all more robust (#16271)

The test is flaky because it checks routes on neighbors immediately after isolating dut. So the test may fail if the neighbors (VM) are not able to process route withdraw in time. Make the test more robust by retrying validation for 60 seconds.

tests/bgp/test_seq_idf_isolation.py

@@ -167,9 +167,9 @@ def test_idf_isolated_withdraw_all(duthosts, rand_one_downlink_duthost,
         # Verify DUT is in isolated-withdraw-all state.
         pytest_assert(IDF_ISOLATED_WITHDRAW_ALL == get_idf_isolation_state(duthost),
                       "DUT is not in isolated_withdraw_all state")
-        pytest_assert(verify_only_loopback_routes_are_announced_to_neighs(duthosts, duthost, nbrs,
-                                                                          traffic_shift_community),
-                      "Failed to verify only loopback route in isolated_withdraw_all state")
+        if not wait_until(60, 3, 0, verify_only_loopback_routes_are_announced_to_neighs,
+                          duthosts, duthost, nbrs, traffic_shift_community):
+            pytest.fail("Failed to verify only loopback route in isolated_withdraw_all state")
     finally:
         # Recover to unisolated state
         duthost.shell("sudo idf_isolation unisolated")