Fix psutils failing to install for heat-cfntools

Reason: tripleo-image-elements/elements/install.d/05-heat-cfntools
        while run from diskimage-builder's dib-run-parts fails to
        find the Python.h header required while compiling psutil.

Change: Include python-dev package in 05-heat-cfntools

Closes-Bug: #1275662

Change-Id: I7ff4cb1e09047ab4184fd62914b51f3cce068f52