Backwards compatibility for node parameter

Adds backwards compatibility for node parameter used by strategies. If
the node value is set by the user configuration it will override the
value for compute_node which is the value used by the strategies now.

This change was introduced in: https://review.opendev.org/#/c/656622/
Resolution discussed in the meeting on the 5th of June 2019
https://eavesdrop.openstack.org/meetings/watcher/2019/watcher.2019-06-05-08.00.log.html

Change-Id: Idaea062789a6b169e64f556fecc34cfbaaee5076

releasenotes/notes/formal-datasource-interface-implementation-222769d55a127d33.yaml

@@ -0,0 +1,17 @@
+---
+features:
+  - |
+    Improved interface for datasource baseclass that better defines expected
+    values and types for parameters and return types of all abstract methods.
+    This allows all strategies to work with every datasource provided the
+    metrics are configured for that given datasource.
+deprecations:
+  - |
+    The new strategy baseclass has significant changes in method parameters
+    and any out-of-tree strategies will have to be adopted.
+  - |
+    Several strategies have changed the `node` parameter to `compute_node` to
+    be better aligned with terminology. These strategies include
+    `basic_consolidation` and `workload_stabilzation`. The `node` parameter
+    will remain supported during Train release and will be removed in the
+    subsequent release.