Fix: Removal tasks' revert methods assume that removal worked

RemoveSelfIP.revert and RemoveSubnetRoute.revert assume that the
SelfIP/subnet route was successfully removed. So restoring can fail
and cause another exception due to HTTP 409 CONFLICT.

Check whether the SelfIP/subnet route was actually deleted before
attempting to restore.

octavia_f5/controller/worker/tasks/f5_tasks.py

@@ -438,6 +438,12 @@ def revert(self, bigip: bigip_restclient.BigIPRestClient,
                         f"was run: {subnet_route_name}")
             return
 
+        # don't restore subnet route if it wasn't removed
+        res = bigip.get(path=f"/mgmt/tm/net/route/~Common~{subnet_route_name}")
+        if res.status_code != 404:
+            LOG.warning(f"Reverting RemoveSubnetRoute: Subnet route {subnet_route_name} was not removed, no need to restore")
+            return
+
         # restore subnet route
         payload = {'name': subnet_route_name,
                    'tmInterface': subnet_route['tmInterface'],
@@ -468,6 +474,12 @@ def revert(self, bigip: bigip_restclient.BigIPRestClient,
                         f"was run: {selfip['name']}")
             return
 
+        # don't restore SelfIP if it wasn't removed
+        res = bigip.get(path=f"/mgmt/tm/net/self/{selfip['port_id']}")
+        if res.status_code != 404:
+            LOG.warning(f"Reverting RemoveSelfIP: SelfIP {selfip['name']} was not removed, no need to restore")
+            return
+
         # restore SelfIP
         payload = {'name': selfip['name'], 'vlan': selfip['vlan'], 'address': selfip['address']}
         LOG.warning(f"Reverting RemoveSelfIP: Restoring SelfIP: {selfip['name']}")