When using an image as the source of new volume the state 'downloading'
prior to the state 'available' is fine.
It is also fine to destroy a volume in the state 'downloading'.
Closes-bug: #2865
Co-Authored-By: Joe Topjian <joe@topjian.net>
This commit follows suit of #1897 by fixing volume-related
parameters which allow the volume attach acceptance test
to work. It also re-enables the volume attach test.
This commit ensures that a volume is detached from all instances
before it is deleted.
It also adds in an `attachment` exported parameter that shows details
of the volume's attachment(s).
