Novaclient shell list command should support a minimal server list

The Nova API supports both a basic (id and name) and detailed server
list, and this is supported in the client by the "detailed=True"
argument to servers.list().  However the shell do_list() method always
leaves this to its default value.  For administrators on a large
system, or where the tenants has a lot of instances a detailed list
can be painfully slow.

This change adds support for a --minimal option to list.

Fixes bug: 1228137

Change-Id: I3126ee6b372606a98f0d7a4e344556f8c05ae224