Fixed the should_gate test.

[petevg]

It was looking in the context, rather than context.config, for the ha
key. This would only fail tests that were failing anyway, but it
clobbered the original Exception, and replaced it with an Exception
raised by my broken check. Whoops.

@kwmonroe @johnsca @abentley @seman

[kwmonroe]

@petevg travis seems to be unhappy with your shenanigans.

[petevg]

@kwmonroe Eek. Had another bug. This time I pushed a more complete fix, along with some proper exit codes. Matrix now exits 101 if it ran into a TestFailure, and stuffs the generic exceptions under a generic exit code of 1. Makes things much easier to test!

[johnsca]

LGTM, but given my review track rating, what do I know? ;)

[kwmonroe]

LGTM, but i learned how to review things from @johnsca, so I haven't actually tested it.