ExtendedS3StorageConfig does not handle missing trailing / in root

[sachin-j-joshi]

Problem description
Current logic in ExtendedS3StorageConfig incorrectly assumes that root has a trailing '/' character. If this is not the case then the S3 storage is wrongly initialized and results in invalid paths/urls.

Problem location
ExtendedS3StorageConfig.java constructor where we initialize values from TypedProperties.

Suggestions for an improvement
Correctly handle the case, by adding the / char when it is missing.