Expose the rebuild preserve-ephemeral extension

This new extension permits preserving the ephemeral partition if the
Nova hypervisor supports that. This is primarily useful when Cinder is
not available to provide preservation of state while replacing the
image in use. One common situation for that is Nova Baremetal.

DocImpact
Blueprint: baremetal-preserve-ephemeral
Partial-Bug: #1174154
Co-Authored-By: Robert Collins <rbtcollins@hp.com>
Change-Id: Ib1511653904d4f95ab03fb471669175127004582
Nova aggregate-details should be more human friendly

'nova aggregate-details' shows Hosts, Availability Zone
and Metadata in the python unicode notation.

+ Adds some tests about aggregates ported from v1 to the
  v3 shell

Change-Id: I69d80b2e76833d78248dee782ae5e53f42a4f4a9
Closes-Bug: #1132961
Merge "Expose the rebuild preserve-ephemeral extension"
Merge "Nova aggregate-details should be more human friendly"