Improve error handling in arc install-certificate
Summary: Fixes T9858. Reasonable typos and misunderstandings currently produce very confusing error messages.
Test Plan:
$ arc install certificate Usage Exception: Server URI "certificate" must include a protocol and domain. It should be in the form "https://phabricator.example.com/".
- Also used a good URI.
- Also used no URI.
Reviewers: joshuaspence, chad
Reviewed By: chad
Maniphest Tasks: T9858
Differential Revision: https://secure.phabricator.com/D14577