Comment 1 for bug 1636150

The default NeCTAR image has python-pbr version 0.7.0 installed on it.
The pip install -r requirements.txt command does not replace this version with the later version required by the application. Hence there are two options: to either uninstall the python-pbr package via apt-get, or to do something along the lines of
sudo pip install --upgrade pbr
before running pip install -r requirements.txt...