The current developer documentation will result in build failures on
Ubuntu. The version of pip packaged for Ubuntu 14.04 can not parse the
project's current requirements.txt files and a couple of dependencies
are missing. This patch aims to add instructions to:
* Add the libssl-dev and libffi-dev dependencies
* Install an updated version of pip
* Remove the deprecated '--no-site-packages' parameter from virtualenv
Change-Id: I6944e5baff67b6e0f0464d7b18d12322968bb2a3
dfca6591b6