test/failing: Wrap failing tests in another harness
test/failing: Wrap failing tests in another harness

Use two harnesses, where the inner harness has failing tests and
writes to a buffer.  The outer harness checks that buffer to ensure
the output is appropriate.  This lets the whole test suite pass:

  $ make
  ...
  All tests successful.
  Files=6, Tests=15,  0 wallclock secs ( 0.05 usr  0.01 sys +  0.00 cusr  0.01 csys =  0.07 CPU)
  Result: PASS

while before this commit it failed:

  $ make
  ...
  Test Summary Report
  -------------------
  test/failing/test   (Wstat: 0 Tests: 2 Failed: 2)
    Failed tests:  1-2
  Files=6, Tests=15,  0 wallclock secs ( 0.05 usr +  0.00 sys =  0.05 CPU)
  Result: FAIL
  Makefile:7: recipe for target 'all' failed
  make: *** [all] Error 1

mndrix/tap.go