Octavia dashboard was skipping pkcs12 bundles when presenting
certificate options for TERMINATED_TLS listeners.
This patch corrects that so that users can select pkcs12 bundles
for use on their listeners.
Change-Id: I83687ed1476a9e413ca6a8a880dd31783450df67
Story: 2005436
Task: 30476
(cherry picked from commit acbaafbbce)