Add a convenience method to get instance volumes

Change-Id: If22cd9245b043f35386ad3c24d46a41b0b8c2c86
Handle instance volume attachments with co-routines

Don't sit in a loop when attaching volumes to instances, use a task that
yields control and allows them to run in parallel - and, in future, in
parallel with other resources being created.

Change-Id: I4653baa87b09a9fb6c2c16b51218f4ea2f2ae6dd
Detach Volumes from an Instance in parallel

Use a PollingTaskGroup to ensure that if there are multiple Volumes
attached to an Instance they are detached in parallel rather than serially.

Change-Id: Ice399ae495af75558f2f8b1b1dc330d0b556a269
Merge "Add a convenience method to get instance volumes"
Merge "Handle instance volume attachments with co-routines"
Merge "Detach Volumes from an Instance in parallel"