try-except shortcut creation, use endpoint specified in profiles.yml for checking/creating shortcuts

[jcvdodson]

cleaning up some issues I found when preparing the demo:

• try-except shortcut creation so that if it fails there is a more informative error message than "failed to connect to Livy" (which also isn't true)
• try-except json parsing for reason above
• use the endpoint specified in profiles.yml (defaulting to public endpoint) for checking whether a shortcut exists and creating it if not