Added some improvements and validations to the s3 unittest
- Added to the load() method from storage a custom config_data support
- Added method check_env_variables() which checks if the environment variables exist in order to avoid error during the s3_storage tests
- Created a patched version of get_size() method on test_s3.py file
- Removed the patch from the S3Storage() class
- Added the moto library to the requirements file
- Added missing decorator above test_errors() method