Updates tox.ini to use new features

tox 1.6 allows us to skip the sdist step, which is slow. This does that.
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: I87f172cfcc44c9afff9c5162791d6c6b31972702
Revert "move rpc_setup to the last step of __init__"

This reverts commit f691ebe03916a78cbf18017d628a28b17f147700.

Change-Id: Idc0bb0e4401e2561f2d8e3132f14df14b7537448
Partial-Bug: #1253896
Merge "Updates tox.ini to use new features"
Merge "Revert "move rpc_setup to the last step of __init__""