Catch exceptions and show error when save template to repo fails.

Fixes [#80215916]

This PR augments the API PR (https://github.com/CenturyLinkLabs/panamax-api/pull/218), to catch the exception raised by `save_template_to_repo`, and displays an error message to the user. Catching the exception here keeps the user on the Save as Template screen, and provides an appropriate context to the error message.
it's probably worth just writing the error here instead of be_true