AWS_BUCKETNAME is only needed in order to write on the bucket, but
read-only access should be allowed for other environments.
Fixes bug introduced by 6c3b610610
With boto (odoo < 12.0) we use an hostname as AWS_HOST.
However with boto3, the connection must be initialized using an
URL containing a scheme (e.g https://)
This commit ensures we can use a simple hostname for odoo >= v12.0
without the need of specifying the scheme in the env var.
Akim Juillerat
