Optimize and re-enable 4085-insufficient-error-message integration test

This test, as it is currently implemented, takes a very long time and is very resource intensive. First it sends a few GB of context to the Docker daemon, then it downloads/extracts a several GB Docker image, then it has to download and install GHC, then build all of Stack, and finally it actually performs its test (which is to make sure there's a reasonable error message if installing GHC fails due to lack of disk space).

Since this is causing trouble on the CI system, I'm disabling the test for now.

I think this can be significantly optimized. If we restrict it to running on Linux only (which I think is reasonable given the Docker image used for the test is Linux based), then the test could mount the already-built `stack` executable from the host into the container (thus skipping most of the setup time and image build context). The container image could be fairly minimal as well -- no need for the whole `fpco/stack-build` image.