Adds volume_driver to the following:
1. api baymodel attribute
2. a new column to the baymodel db
3. objects.Note: Updates baymodel object version
4. Unit tests
Co-Authored By: Kai Qiang Wu(Kennan)<wkqwu@cn.ibm.com>
Co-Authored By: Ton Ngo<ton@us.ibm.com>
Partially-Implements: blueprint magnum-integrate-with-cinder
Change-Id: I25506bd39ab4be513ef99c39f8c52a502b300d92