Removes disk-config extension from v3 api

This patch removes disk-config extension for v3 api, and also
remove related tests. And remove resize extension point for
servers core because there isn't any extension using it anymore
and there isn't good way to test resize extension point.

Implements bp api-v3-remove-disk-config
DocImpact

Change-Id: I894ae6f4e0d6c9f956a71e8e061ccb3fa1b039d8
Merge "Removes disk-config extension from v3 api"