[REVIEW] S3 scraper fix

The S3 scraper is broken, if the bucket being listed would return "paged" response (when the repository has over 1000 unique files in it). The paging logic was creating broken URLs, resulting in having only 1st page fetched, and used to build prefixes file. More about it in the linked issue.

Related issue:
https://issues.sonatype.org/browse/NEXUS-5698