The help message of command "openstack volume show" accepts either
volume-name or volume-ID. But the metavar is "volume-id" as below.
It can easily lead to misunderstanding.
usage: openstack volume show [-h] [-f {json,shell,table,value,yaml}]
[-c COLUMN] [--max-width <integer>]
[--noindent][--prefix PREFIX]
<volume-id>
Change-Id: I57576ea23868b1026cf268be69b39e98a53aafd4