Updated openstack/openstack
Project: openstack/python-heatclient  bc11c74fe0dfad0e426d4c0eeb334a18846f3984
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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: Ib51796afbfdffb5a879046ca1b94a55b1f6ef6f1