exec_test: don't emit output

[imjasonh]

Storing up to 1KB of output for each exec in TF state makes it unnecessarily large and unnecessarily slow to marshal/unmarshal.

If you want to check details of the output, you can do that with existing tools inside the shell environment.

This output was also used by our own provider tests to check that free ports worked, but that's no reason to keep it around. The free port test still heuristically checks that N simultaneous free-ported docker runs don't conflict, which is probably good enough.

[xnox]

So this means that none of our test cases ever produce any output that one can later audit. Is it possible to use like output terraform module to store the test results somewhere else? Or does even output stuff end up being serialized inside the terraform state file?

[mattmoor]

output is serialized into state :(