Remove/reduce global python dependancies

[smesdaghi]

python packages such as osgeo (gdal wrappers) and httplib2 (ssl certificates) are getting installed in the global python. httplib2 didn't used to get installed under 12.04 but under virtual boxe's 14.04 it is already installed globally. Other 14.04 images (like the one used for noblis servers) do not have it installed either. This means that geonode (or something along the way) ends up bringing it in and installing it under the geonode virtual environment at /var/lib/geonode. As a result, when the ssl certs need to be installed in the httplib2 package, their location can be different and therefore cause an error/early termination of the installation process.

We need to make sure that python libraries that geoshape depend are are installed under the geonode virtual environment to reduce changes of the install not working when different os images/versions are used. This is a bit easier said than done because of other install order dependancies but worth doing.

Note that the /var/lib/geonode python environment is linked to the global python through /var/lib/geonode/lib/python2.7/site-packages/_virtualenv_path_extensions.pth. Once we remove dependency of on the global python, we should remove the entry in the virtualenv path extension.