add is_s3_upstream() to cvmfs_server
`cvmfs_server check` is S3 aware
FIX: integration test 514 for S3
allow for S3 repos in test_functions::create_repo()
FIX: check_catalog_presence() and get_catalog_count()
show storage type in `cvmfs_server list`
remove unused variable upstream_path_
Cosmetics: replace tab indentation by spaces