Added type description for volume type client

This patch added client handling and unit tests for volume type description:

* Added 2 client methods for volume type.
  default: to get the default volume type
  update: to upate an existing volume type to update description

* Added 2 new command-line operations.
  type-update (adminitrator only)
  type-default

* type-list should display description.

* type-create should have an option for entering the description.

The corresponding cinder APIs change volume-type-description:
https://review.openstack.org/#/c/131871/

Implements: blueprint volume-type-description
Change-Id: I2735d7050d90589d19f45e21096577febdcca8bb