Test framework relies on ancient libjsoncpp

[ianamason]

The latest libjsoncpp package installed by default on 16.04 is 1.7.2.
Stoke seems to rely on 0.6.0 which is hard to find (I found 0.7.0 on
their GitHub page).

The tests do not compile with the latest on 16.04 (using gcc 4.9).

[bchurchill]

If you want to fix this, pull requests are welcome! It's probably not too much work to avoid using json in the test suite all together. This is also a good ticket for someone new to the project. At this point we aren't planning on actively supporting this work, and we've mainly focused on packaging via docker to create a consistent environment.