Update volume type name for volume type API

Update volume type name for volume type API

This continues the change for updating volume type to
include changing name.

- Updated the following APIs and tests for volume type

* update volume type
PUT http://<openstackhost>:8776/v2/${tenant_id}/types/${vol_type_id}
body
{
    "volume_type": {
      "name": "test_updated",
      "description":"updated_desc"
    }
}

** user can update name
** if update name, name can not be empty spaces.
** if update name, can not change the name to be the same as the one
in another volume type
** name and description can not be both None

Implements: blueprint volume-type-description
Change-Id: Idc08f796932df709ff20c17f6bc8d4753d85ad3c