'juju run' on leader if no unit specified

[Alex Lutay]

Hi,

Proposal: is it possible to allow 'juju run' on leader if no unit specified?
Example: 'juju run mysql list-backups' will be the same as 'juju run mysql/leader list-backups'.

It will improve UX a lot without any negative implications, IMHO:
 * often when you have single unit app, you have to use /0 (or /leader which is even longer).
 * often you do not care about the unit to execute action: `juju run grafana get-credentials`
 * less to type and less to read
 * one rule to remember: specify the unit to execute your action, otherwise leader will be choosen.
 * more fun with Juju!

Thank you!

P.S. Based on Pietro great jhack improvement here: https://github.com/canonical/jhack/pull/143/files

P.P.S. the same logic also will be useful for `juju ssh`, `juju exec`, ...

[Ian Booth (wallyworld)]

This is an interesting idea. It seems like a nice UX improvement.