Always print out the nested command on failure. (#1952)
Always print out the nested command on failure. (#1952)

* Always print out the nested command on failure.

* Gate debug info under the verbosity flag.

* Fixing flake8 errors.

googledatalab/datalab,googledatalab/datalab,googledatalab/datalab,googledatalab/datalab,googledatalab/datalab,parthea/datalab,parthea/datalab,parthea/datalab,parthea/datalab,googledatalab/datalab,parthea/datalab,parthea/datalab