Review S3_PING impl with the CloudBasedDiscovery.txt design

[rhusar]

Validate S3_PING impl with the generic CloudBasedDiscovery design.

[rhusar]

Basically the question is that when the s3 objects are iterated over, in case of a failure to parse a file the loop simply breaks while in e.g. FILE_PING it continues to parse. This needs to be evaluated if this is resilient enough.

[rhusar]

Hm, we should also review org.jgroups.protocols.FILE_PING#remove_old_coords_on_view_change and org.jgroups.protocols.FILE_PING#remove_all_data_on_view_change are false by default - does that mean that old coordinators just keep leaving their files around slowly slowing down the discovery?