When spawning the pebble and pebble-challtestserv processes redirect stdout/stderr to bytes.Buffer instances and print their content at test end as appropriate. The stdout/stderr content for each process is printed if the test failed, or if testing is being done in verbose mode. Otherwise the output is swallowed. This makes debugging test failures much easier as output from the subprocesses from independent tests isn't intermingled. Updates golang/go#74437 Cq-Include-Trybots: luci.golang.try:x_crypto-gotip-linux-amd64-longtest Change-Id: Ia79a3609ce3522ef6248442de247554c39367162 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/686935 Auto-Submit: Daniel McCarney <daniel@binaryparadox.net> Reviewed-by: Roland Shoemaker <roland@golang.org> Reviewed-by: Carlos Amedee <carlos@golang.org> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>