Enable usage of proxies defined in environment (http(s)_proxy).

As far as proxies usage is concerned, keystone-client API and swift-client API behave differently because the former uses python Request library while the latter uses raw httplib. As a result, Keystone authentication honors environment variables http_proxy, https_proxy and no_proxy while Swift doesn't.

This patch, which code is mainly borrowed from Python Requests, makes Swift
data connections and Swift authentication connections behaving homogeneously.

Change-Id: Ic8a0089c35c458d7ed96e572e22429014298fe4c
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 were not
asking for.

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

Change-Id: Id751f7d5d40a80d348a5f5936539d9462b40b14b
Merge "Enable usage of proxies defined in environment (http(s)_proxy)."
Merge "Updates tox.ini to use new features"