Add a tox job for generating docs

Add a tox job to make it easier for developers to generate their
own docs before submitting a patch.

Change-Id: Icbfd5ee5556a9c344ebe9ca7f4b579a87ad2d01b
Fix the return code of the command reset-state

Currently, the command reset-state return code is zero if it
failed for any of volumes, it should be nonzero.

Change-Id: Ic6da238861fd003375003399bc6def6bf860a015
Closes-Bug: #1339643
Merge "Fix the return code of the command reset-state"
Merge "Add a tox job for generating docs"