Adds disk_format parameter to upload_volume method in volumes client

Adds a third parameter, disk_format, to the upload_volume method of
the volumes client. The parameter is also added to the Tempest
configuration and defaults to "raw" if not set.

Closes-Bug: #1218666
Change-Id: I6c62796161c9219cbd80eb9fecc7fbb0f3a4681a
Merge "Adds disk_format parameter to upload_volume method in volumes client"