Initial version of Savanna v0.2

* pluggable provisioning mechanism
* a lot of old code has been removed
* new version of REST API (1.0)
* image registry draft implemented as novaclient extension
* oslo updated
* using oslo.db instead of flask-sqlalchemy
* some hacking fixes
* using alembic for db migrations

Partially implements blueprint pluggable-cluster-provisioning.
Partially implements blueprint savanna-rest-api-1-0.
Implements blueprint hadoop-image-registry.
Implements blueprint fulfill-openstack-requirements.
Implements blueprint db-migrate-support.

Change-Id: I5df80d67e25c2f4f8367f78f67fb9e9e76fc3647