Implement 'personality' plugin for V2.1

User can specify 'personality' attribute while server creation
& rebuild to inject files into server.

This patch implement this as separate plugin for V2.1 API.

Also define the schema and unit tests for the same.

Partially implements blueprint v2-on-v3-api

Change-Id: Ia0c527539af7fe33eba4999822476653e1b96bc6
Merge "Implement 'personality' plugin for V2.1"