Updates tox.ini so that both v1 and v2 are built

Discussion with Vish Ishaya reveals that grizzly clouds still use
Volume API v1 and need to refer to this document.

Change-Id: Id5b574e5bcbb70fe9f9d9295cbafab980e275150
Partial-Bug: 1298049
Merge "Updates tox.ini so that both v1 and v2 are built"