Python Savanna Client initial implementation

Image Registry:
* Register Images and Tags
* Edit existing Images and Tags
* Unregister Images

Supports create, read and delete operations for:
* Node Group Templates
* Cluster Templates
* Clusters

No CLI support

Implements blueprint python-savannaclient

Change-Id: If0b7c4fb9660d646cb37c4b224bdcf39dc61bb19