workspace_on_error starting message

[stemangiola]

@myushen, could you please have a look at how workspace_on_error works in targets, and if TRUE in HPCell prints a message when the pipeline starts, of what to type if a step produces an error?

For example

HPCell says: workspace_on_error was set to true. If a target (e.g foo) causes error, please execute XXXXX in the console to open the etc..etc.. 

use the same terminology as targets documentation.

Thanks, so Will can debug an error he identified

FYI @william-hutchison