Updates tox.ini to use new features

Reasons:
 - tox update v1.6

Changes:
 - tox 1.6 allows us to skip the sdist step, which is slow.
 - It also allows us to override the install line. In this case, it's
   important as it allows us to stop getting pre-release software we
   weren't asking for.

Original patch by Monty Taylor, talked about here:
http://lists.openstack.org/pipermail/openstack-dev/2013-September/015495.html

Change-Id: I8a8fdd420eceb5b702e7d9eedd8b5be341d3f56e
Discrepancy between README.rst and cinder help

1) --version in README should be --os-volume-api-version

2) CINDER_URL should be OS_AUTH_URL

Change-Id: I409634f3025463f2ae9419ddd0d99fa50554a04d
Closes-Bug: 1251385
Merge "Updates tox.ini to use new features"
Merge "Discrepancy between README.rst and cinder help"