Don't run `clever deploy` if the app is up-to-date

Don't run `clever deploy` if the app is up-to-date

Running `git push` when the remote is up-to-date
no-ops (it does not trigger a deployment, but it does not fail either).

Running `clever deploy` when the remote is up-to-date triggers a failure. Here, we care about the _end result_ (ie the app is deployed on the correct commit), so no-oping is more appropriate.

This behaviour is not baked in `clever-tools`, but I think it should. I opened an issue. This script
is a temporary workaround. (at least I hope it's temporary)
https://github.com/CleverCloud/clever-tools/issues/422