Cert: Add --verbose mode to dumps logs from subprocesses to STDOUT

* Add "verbose_mode" option in test config JSON
* Add --verbose mode in gd/cert/run script
* In verbose mode, logs from cert stack, stack under test, and
  root-canal will all be dumped to STDOUT with color coded headers
* In implementation, ThreadpoolExecutors were created to run logging
  thread at back-end

Bug: 156038378
Test: gd/cert/run --host --verbose
Tag: #gd-refactor
Change-Id: Id9619775392517b13f60a5108b441c3e6df9ce8f