Add mgmt API for datastores

Implemented API calls and shell commands for create/update
datastores/versions.

DocImpact: added CLI for datastores version management
Depends-On: I01c0ecc276a73fbbc06ec39bfaa1c66f47fc3a9c

Change-Id: Iee7ed7b141548ef64231acad6319e769d356b97f
Partially Implements: blueprint datastores-mgmt-api