HTTP(S) proxy can be specified when creating the template.
https://docs.openstack.org/magnum/latest/admin/magnum-proxy.html
However, it is not being utilized when talking to a public etcd discovery
service, which result in failed cluster creation. We need to be able to
use HTTP(S) proxy when services are running behind a firewall.
NOTE: this patch also updated some test cases to explicitly set
the proper HTTP status code in the mock HTTP request as by default
they are not be initialized, which caused those tests to fail.
Change-Id: I13d86b0dc7c232a51149107f0412219388d8c2cd
story: 2004664
(cherry picked from commit ffc61816c8)
f86de684d2