Tidy up - Watcher Decision Engine package

Some Python class and packages need to be renamed
for a better compliance with the shared terminology
which provides a better understanding of Watcher
objects and components by every contributor.

This patchset is there to change the code structure by adding the folder
"strategies" and "loading".

Partially implements: blueprint glossary-related-refactoring

Change-Id: I56fb24ee6762b3186eccde5983233e17bb227cc1

watcher/tests/decision_engine/messaging/test_audit_endpoint.py

@@ -22,7 +22,7 @@ from watcher.decision_engine.messaging.audit_endpoint import AuditEndpoint
 from watcher.metrics_engine.cluster_model_collector.manager import \
     CollectorManager
 from watcher.tests import base
-from watcher.tests.decision_engine.faker_cluster_state import \
+from watcher.tests.decision_engine.strategy.strategies.faker_cluster_state import \
     FakerModelCollector