pin django to 1.4.x stream

django 1.5 just released in the last hour, and there is a
compatibility issue with it and horizon causing gate failures.

Pin this so that we can get back to business and let the horizon
team address django 1.5 when it makes sense to them.

Change-Id: I6ddf9623f8a4719b1cb82b118c1876373051fd28