Add 3 secs to wait for keepalived state change

We add 3 seconds to the keepalived state change to avoid timeout
failures in test_read_queue_change_state.

Change-Id: Ic54bd6f699b91b53f22c93c972d8def6c99d0eb7
Closes-Bug: #2035382
Related-Bug: #2003022
(cherry picked from commit f28e416)

Author: Miguel Lavalle

neutron/tests/functional/agent/l3/test_keepalived_state_change.py

@@ -96,7 +96,7 @@ def text_in_file():
             except FileNotFoundError:
                 return False
         try:
-            utils.wait_until_true(text_in_file, timeout=15)
+            utils.wait_until_true(text_in_file, timeout=18)
         except utils.WaitTimeout:
             devices = {}
             for dev in ip_lib.IPWrapper(