make url protocol flexible between http/https

[DustinKLo]

currently osaka's s3 storage class is hardcoded to write to s3 with the https protocol: https://github.com/hysds/osaka/blob/develop/osaka/storage/s3.py#L70
but if we're running a local minio server then using https will result in an SSL error:

botocore.exceptions.SSLError: SSL validation failed for https://minio:9000/datasets [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1129)

will look into finding a way to make this configurable, either through celeryconfig.py or other means

the previous change can be tracked here: #20