Fix the amphora base port coming up

A recent change[1] broke the base port IP address coming up in the
amphora. This would cause active/standby and single topology amphora
with members on the VIP subnet to fail.

This patch resolves this issue by not flushing the eth1:0 address.

Story: 2005383
Task: 30368

[1] https://review.openstack.org/#/c/648504/

Change-Id: I52e7e9f172b7783bae09be76cc137f4e7198165f

octavia/amphorae/backends/agent/api_server/osutils.py

@@ -199,7 +199,7 @@ class BaseOS(object):
         return host_routes
 
     @classmethod
-    def _bring_if_up(cls, interface, what):
+    def _bring_if_up(cls, interface, what, flush=True):
         # Note, we are not using pyroute2 for this as it is not /etc/netns
         # aware.
         # Work around for bug:
@@ -215,9 +215,10 @@ class BaseOS(object):
             out = subprocess.check_output(int_up.split(),
                                           stderr=subprocess.STDOUT)
             LOG.debug(out)
-            out = subprocess.check_output(addr_flush.split(),
-                                          stderr=subprocess.STDOUT)
-            LOG.debug(out)
+            if flush:
+                out = subprocess.check_output(addr_flush.split(),
+                                              stderr=subprocess.STDOUT)
+                LOG.debug(out)
             out = subprocess.check_output(cmd.split(),
                                           stderr=subprocess.STDOUT)
             LOG.debug(out)
@@ -248,7 +249,7 @@ class BaseOS(object):
             cls._bring_if_down(secondary_interface)
         cls._bring_if_up(primary_interface, 'VIP')
         if secondary_interface:
-            cls._bring_if_up(secondary_interface, 'VIP')
+            cls._bring_if_up(secondary_interface, 'VIP', flush=False)
 
     def has_ifup_all(self):
         return True

releasenotes/notes/fix-eth1-ip-flush-7fadda4bdca387b5.yaml

@@ -0,0 +1,11 @@
+---
+upgrade:
+  - |
+    To fix the issue with active/standby load balancers or single topology
+    load balancers with members on the VIP subnet, you need to update the
+    amphora image.
+critical:
+  - |
+    Fixed a bug where active/standby load balancers and single topology
+    load balancers with members on the VIP subnet may fail. An updated
+    image is required to fix this bug.