This moves off use of the purged s3a://landsat-pds bucket, so fixing tests
which had started failing.
* Adds a new class, PublicDatasetTestUtils to manage the use of public datasets.
* The new test bucket s3a://usgs-landsat/ is requester pays, so depends upon
HADOOP-14661.
Consult the updated test documentation when running against other S3 stores.
Contributed by Daniel Carl Jones
Change-Id: Ie8585e4d9b67667f8cb80b2970225d79a4f8d257
4230162a76