Code review comment for lp://staging/~dpb/latch-test/dont-test-so-much

I am getting a lint error on "make lint":

./latch.py:197:33: E901 SyntaxError: invalid syntax
./test_latch.py:73:1: E302 expected 2 blank lines, found 1
Makefile:8: recipe for target 'lint' failed
make: *** [lint] Error 1

This might be due to python3 being default on xenial, but it's easy enough to fix, so please do that (wrap print parameters on line 197 inside parentheses).

A few other nits inline, but overall a nice change: thanks for doing this work!