Show a nicer message when learntris implementation times out.

[tangentstorm]

Given the following learntris:

#!/usr/bin/env python
while True: pass

...testris produces the following output:

Running test 1: io.q
q : quit
---- sending commands ----
q
---- awaiting results ----
Test 1 failed: <program timed out>

It's probably for the best that the normal explanatory text for the test is missing, since the student should be working on handling 'q' correctly, or removing an accidental infinite loop.

However, there should be some explanation about exactly what timeouts are (i.e. that their implementation took too long to respond and could be locked up.) and probably a reminder about the q command.

(See discussion and notes from @mattpul in #25)