Be more resilent regarding error handling, log and report errors.

[Filirom1]

Curently there is no warning/error if curl fails to send a file to S3 (Not Authorized error for exemple).
This is an exemple, but we could make this bash script more resilent.

Echo are printed to the user via the git connexion.

We need more logs to debug, but the user do not want to be bothered with a tons of logs if everything works great. Check what kind of logs are written by Heroku when everything is alright, when the Procfile is missing, when unable to compile the slug, ...