Tester should print out why a test failed

[kevin1]

Current: debug: ❎ array_basic.nh Proposed: debug: ❎ array_basic.nh (Reason string)

where "Reason string" can be:

• Incorrect output
• nhc failed
• clang failed
• Nonzero exit code

And we could sum up the number of each kind of failure at the end