Improve exception visibility within console

When exceptions are encountered the console displayed message often includes Parsl information (which app failed and workflow-wise why it failed) but this sometimes does not include information about what specifically failed. This may leave the audience with an understanding that something went wrong but without an understanding of how it fix or share it with others (without further consulting with the log file(s)). This issue highlights the need to raise nested exceptions from within the Parsl apps to provide better visibility and quicker troubleshooting. Inspired from conversations in #52 .