amphorav2 driver was introduced in stable/ussuri in Octavia, but some
parameters to configure the backend server to enable persistence were
still missing in puppet-octavia.
Change-Id: I8a9bf0b2c17cd35bc09fbb0270c4ef4ed4e491bd
(cherry picked from commit 2b9f2a0813)
(cherry picked from commit 034d66f58b)