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: Idbf8e08383232ae0af5b245c1abe91a7f852bfcf
Fix and enable gating on H306

H306 - module imports should be in alphabetical order

Change-Id: I1f8fc25b0e6ca23c21c90bda420f42a45141c2e2
Merge "Updates tox.ini to use new features"
Merge "Fix and enable gating on H306"