Make availability_zone in aggregate_create optional

Aggregates do not require an availability zone any more, but in order to
keep the current API, allow for availability zone to be set to None (the new
default value)

Fixes bug 1123468

Change-Id: I216c4fc808a91b0a5f602ee02ae1bca46adb73f4
Fix nova availability-zone-list for admin users

Don't need to convert returned timestamp

Fix bug 1123381

Change-Id: I1dbc82475b44b8d321fffb512083fc7a3b13153d
Expand and improve baremetal API.

This adds an additional command to list the interfaces associated with a
baremetal node.

It also fixes some docstrings and renames the existing interface
commands to be more consistent with the node commands.

Change-Id: Ia6ae383d76adb1c9d632bf69ec22438f1412c66f
Merge "Make availability_zone in aggregate_create optional"
Merge "Fix nova availability-zone-list for admin users"
Merge "Expand and improve baremetal API."