Remove pygraphviz due to this problem:

    Your Graphviz installation could not be found.

    1) You don't have Graphviz installed:
       Install Graphviz (http://graphviz.org)

    2) Your Graphviz package might incomplete.
       Install the binary development subpackage (e.g. libgraphviz-dev or similar.)

    3) You are using Windows
       There are no PyGraphviz binary packages for Windows but you might be
       able to build it from this source.  See
       http://networkx.lanl.gov/pygraphviz/reference/faq.html

Same as in this thread: https://groups.google.com/forum/#!topic/tardis-devel/h4lNDN148og

I have no idea why this popped up today. Builds have been fine for a few weeks.
Add pygraphviz packages (not really needed) and the image-trove config and binary.