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)
diff --git a/releasenotes/notes/Placement-client-for-placement-based-minimum-bw-allocation-27ed0938118752b6.yaml b/releasenotes/notes/Placement-client-for-placement-based-minimum-bw-allocation-27ed0938118752b6.yaml
new file mode 100644
index 0000000..21b74a6
--- /dev/null
+++ b/releasenotes/notes/Placement-client-for-placement-based-minimum-bw-allocation-27ed0938118752b6.yaml
@@ -0,0 +1,17 @@
+---
+features:
+  - |
+    Add basic read-only Placement client to Tempest to make possible the
+    testing of the placement based bandwidth allocation feature.
+    The following API calls are available for tempest from now:
+
+    * GET /allocation_candidates
+    * GET /allocations/{consumer_uuid}
+
+    Add new config group ``placement``, with the config options:
+
+    * ``endpoint_type`` to use for communication with placement service.
+    * ``catalog_type`` of the placement service.
+    * ``region`` as the placement region name to use.
+    * ``min_microversion`` and ``max_microversion`` as the range between
+      placement API requests are sent.