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
Follow rename of files in api-site

api-site renamed volume-api.wadl to volume-api-v2.wadl, rename links to
the files.

Change-Id: I416020da7b5a2d30d78775acbb1af1fbdd979171
Merge "Updates tox.ini so that both v1 and v2 are built"