Pick stale amphora randomly
Pick stale amphora randomly

Avoid getting the same amphora all the time if its loadbalancer
stuck in PENDING state and could not be failovered.

Story: 2007340
Task: 38877

Change-Id: I2f680a00be695c3828166e6803882765af79b79e

openstack/octavia,openstack/octavia,openstack/octavia