Fix help messages for name arguments

Users can specify the name of an instance as the argument, which are
passed through find_resource(), instead of the id.
This patch changes some help messages for explaining this behavior.

Related-Bug: #1220590

Change-Id: I9af1259af4319b82b94d7b28536def3107ec5dd5
Add volume name arguments

This patch adds volume name arguments to the following subcommands:
 * snapshot-create
 * backup-create
 * backup-restore
 * transfer-create

Fixes bug #1220590

Change-Id: Ib0ff6e62d45abb14fa8c7313511ef6f72befe0d5
Merge "Fix help messages for name arguments"
Merge "Add volume name arguments"