Test rediscovering for redeployed cluster fix

In models.py file descriprion of new entity called ClusterState was
added. This new entity stores info about current cluster state (its
deployment tags). Function discovery_check has been modified: logic that
controlls rediscovering of tests for redeployed cluster has been
changed. It now is based on data from ClusterState. Unit tests have been
fixed in orded to support new logic. New initial alembic migration has
been created (cluster_state entity is included).

Rediscovering logic has been fixed.

Change-Id: I61bf4d56a097a49413c494adee5587cfad83949c
Merge "Test rediscovering for redeployed cluster fix"