When using subnets with host_routes in amphorav2, the host_routes
attribute in the Subnet data structure was not correctly converted to a
HostRoute data structure. It triggered exceptions and failed to
provision the load balancer.
Story 2008738
Task 42092
Change-Id: I39391070cea170a6039f901093f09fc89ba06123
(cherry picked from commit d0ec3aaf23)