Add downstream octavia source for testing

Author: seunghun1ee

etc/kayobe/kolla.yml

@@ -146,6 +146,10 @@ kolla_sources:
     type: git
     location: https://github.com/stackhpc/networking-mlnx
     reference: stackhpc/{{ openstack_release }}
+  octavia:
+    type: git
+    location: https://github.com/stackhpc/octavia.git
+    reference: fix-octavia-api-certificate
 
 ###############################################################################
 # Kolla image build configuration.