This patch refactors the failover flows to improve the performance
and reliability of failovers in Octavia.
Specific improvements are:
* More tasks and flows will retry when other OpenStack services are
failing.
* Failover can now succeed even when all of the amphora are missing
for a given load balancer.
* It will check and repair the load balancer VIP should the VIP
port(s) become corrupted in neutron.
* It will cleanup extra resources that may be associated with a
load balancer in the event of a cloud service failure.
This patch also removes some dead code.
Change-Id: I04cb2f1f10ec566298834f81df0cf8b100ca916c
Story: 2003084
Task: 23166
Story: 2004440
Task: 28108
955bb88406