Install PyPi dependencies alongside apt ones for dib elements

The python-novaclient package in apt is really old (2012.1-0ubuntu1)
and has a pinned dependency on prettytable 0.5. All of the newer
clients have a dependency on prettytable 0.6 - 0.8. This is causing
issues on the guest agent.

This updates the dib elements so that dependencies from PyPi are
installed alongside apt dependencies.

Fixes bug 1189641

Change-Id: I5233aad2045cbec8610569c40e50bf26defe2dfa
Merge "Install PyPi dependencies alongside apt ones for dib elements"