Get Sikuli + Robot Framework to run in a virtual machine

See e.g. [this SO thread](https://stackoverflow.com/questions/39996130/run-robotframework-tests-with-sikuli-library-with-jenkins-on-vm-rdc). We don't even need Jenkins; if the test could run on a local VM (either visible on a second screen or minimized) without hijacking keyboard input, it would be good enough.