Move volume specific Admin CLI operations to a new "volume" option

[shaominchen]

Currently Admin CLI has the following top-level options: {ls, policy, tenant, set, status}

Among these options, "ls" and "set" are volume specific operations. I think it's clearer and more organized to move those 2 to a new top-level "volume" option, i.e.

vmdkops_admin volume ls...
vmdkops_admin volume set...

This will also avoid confusion when we need to add other new top-level command options.

[govint]

This is what we have today and this issue seems to be fixed.

/usr/lib/vmware/vmdkops/bin/vmdkops_admin.py
usage: vmdkops_admin.py [-h] [--output-format OUTPUT_FORMAT]
{config,policy,volume,status,vmgroup} ...

vSphere Docker Volume Service admin CLI

optional arguments:
-h, --help show this help message and exit
--output-format OUTPUT_FORMAT
Specify output format. Supported format : xml. Default
one is plaintext

Manage VMDK-based Volumes for Docker:

{config,policy,volume,status,vmgroup}
action
config Init and manage Config DB to enable quotas and access
control [EXPERIMENTAL]
policy Configure and display storage policy information
volume Manipulate volumes
status Show the status of the vmdk_ops service
vmgroup Administer and monitor volume access control