base clean Ubuntu 12.04LTS clean-up changes for install

Note: this includes a couple of lines Xavier has pull-requested also (by necessity);

install-system-req.sh: remove rvm install,
   as later removed in create-dev-env;
   mv common platform installs so they work for Linux too;

create-dev-env.sh: update default WORKON_HOME
   to match virtualenv docs, consistent;
   fix Linux case selectors;
   fix sourcing of virtualenvwrapper;
   fix rvm installation call;