Fix authentication bug when booting an server in V3

Currently when booting a server with V3, novaclient sends an empty
os_password to image_cs. This will cause 401(Unauthorized: Invalid
user/password) when trying to find image. This is is a result of
changes nova's V3 API: nova is no longer used as a proxy for the
image service. So novaclient uses two Client instances: one for
nova, the other for image service. This patch checks os_password
before creating the image Client and assigns it if it's empty.

Change-Id: Ic54cef93e9b823fb98b1edd78776c9a1fc06ba46
Closes-Bug: #1277425
Nova CLI for server groups

CLI support for blueprint instance-group-api-extension

REST API support:- https://review.openstack.org/#/c/62557/

DocImpact
 - supports create, list, get and delete
 - only V2 is supported

Change-Id: Iaa5a2922b9a0eed9f682b7584c2acf582379b422
Avoid AttributeError in servers.Server.__repr__

servers.Server represents various object now, and some of them may
don't have attribute 'name', for example, the interface_list() result
object. It will cause AttributeError when we try to format string with
such object, so I add a check for the 'name' attribute in __repr__
method, it will use 'unknown-name' instead when 'name' is not found.

Change-Id: If4757d5d73721774543d58a4cc875710a6013f34
Closes-Bug: #1280453
Enable delete multiple server groups in one request

Currently, "nova server-group-delete" can only delete one server
group in one request, this patch was enabling nova client support
removing multiple server groups in one request.

Change-Id: I373151bc27cbe8617e2023ba99f6fb3f0108d592
Closes-Bug: #1302954

Conflicts:
	novaclient/tests/v1_1/test_shell.py