Implements base classes  for storage controllers

This patch follows (or should follow) the specs written in the v1
specification: https://wiki.openstack.org/wiki/Marconi/specs/api/v1

This patch deletes driver_base.py and adds base.py in marconi/storage
package.

Note: Most of this implementations will be tested in further patches
since there's no good way to test these base classes.

Implements blueprint storage-base

Change-Id: Iefa6374635fcf9dd9fc60417d8ed5c306bbc619a
Merge "Implements base classes  for storage controllers"