EmptyCatalog error should give helpful message

[msherman64]

Currently we print a traceback on an EmptyCatalog error. We should print a useful message instead. Example:

except keystoneauth1.exceptions.EmptyCatalog as ex:
    print("Received empty catalog error, make sure you are authenticated to a site.")

[BNNARAJ]

Hello, @msherman64 sir,
I want to resolve this issue,can you please navigate me to the code file in which I can change this error message and make it more meaningful