Pass environment variables of proxy to tox
Pass environment variables of proxy to tox

When a development environment is under a proxy, tox fails even
when the environment variables are set.

This patch fixes the problem by passing them on to the env.

Change-Id: I903a023918d48e4cd9625576522c4df7d118949b
Closes-Bug: #1465086

pombredanne/bandit,chair6/bandit,pombredanne/bandit,stackforge/bandit,stackforge/bandit