Hide the "Host Aggregates" admin panel if not enabled

This checks ether the extension is supported in nova and disables
access to the panel (hiding it) if not.

Closes-Bug: #1332066
Change-Id: Ie6f5ec7a833d489adca6d56f34a39579e9eabdde
Merge "Hide the "Host Aggregates" admin panel if not enabled"