Port disk_config extension for V2.1

This patch ports v2 disk_config extension to v2.1.

Unittest code modified to share testing with both v2/v2.1.
API sample file and their tests have been added.

Also added extension point of server resize V3.

Partially implements blueprint v2-on-v3-api

Change-Id: Id2aace8121a310f8c86c6a9cc532bd1074d653c4
Cleanup tenant networks plugin config creation

Cleans up the os-tenant-networks plugin config creation.
Although written in a way that the config options could be
declared in multiple places in Nova this is no longer the case
and its not something we should do anyway.

This is some prep work before porting the plugin to the
v2.1 API

Partially implements blueprint v2-on-v3-api

Change-Id: I3b8b26035654f2482b3ba9561c404b6a437ec8a2
Merge "Cleanup tenant networks plugin config creation"
Merge "Port disk_config extension for V2.1"