Fix the image name of a shelved server

The shelve feature powers a server off, and creates a snapshot of the
server. The snapshot image name is "instance-XXXXXXXXX-shelved" and it
doesn't contain a server name like the following:

  $ nova list
  +----+------+--------+------------+-------------+------------------+
  | ID | Name | Status | Task State | Power State | Networks         |
  +----+------+--------+------------+-------------+------------------+
  | .. | vm01 | ACTIVE | None       | Running     | private=10.0.0.5 |
  +----+------+--------+------------+-------------+------------------+
  $ nova shelve vm01
  $ nova image-list
  +----+---------------------------------+--------+--------+
  | ID | Name                            | Status | Server |
  +----+---------------------------------+--------+--------+
  | .. | instance-00000004-shelved       | ACTIVE | ..     |
  +----+---------------------------------+--------+--------+
  $

"instance-XXXXXXXXX" is OS-EXT-SRV-ATTR:instance_name, and a non-admin
cannot see it.

This patch changes the name to "<server name>-shelved", so that a non-
admin user can know the server name of a shelved image:

  $ nova image-list
  +----+--------------------+--------+--------+
  | ID | Name               | Status | Server |
  +----+--------------------+--------+--------+
  | .. | vm01-shelved       | ACTIVE | ..     |
  +----+--------------------+--------+--------+
  $

Closes-Bug: 1232991

Change-Id: Idc73658e29cb77dfcc8b046535a36affc1831605
Merge "Fix the image name of a shelved server"