This commit cleans up the volume and block device handling in the instance
resource. It also adds more acceptance tests to deal with different workflows
of attaching and detaching a volume through the instance's lifecycle.
No new functionality has been added.
This commit fixes the previously broken "boot from volume" feature. It also
adds an acceptance test to ensure the feature continues to work.
The "delete_on_termination" option was also added.
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.
