Add placement client for basic GET operations

The goal of this placement client for tempest is to make possible the
end-to-end testing of the placement based bandwidth feature (see the
nova and neutron specs: https://review.openstack.org/502306
https://review.openstack.org/508149)
The minimum placement microversion is 1.29, and the following operations
are supported: list_allocation_candidates, list_allocations.

Change-Id: I0cf1caadeb40761ec79338510919f12baf2d8f56
Partial-Bug: #1578989
See-Also: https://review.openstack.org/502306 (nova spec)
See-Also: https://review.openstack.org/508149 (neutron spec)
8 files changed