Should fail gracefully when unable to fetch ACL/owner info

[ryan-williams]

S3Utils. getS3ObjectSummary makes a second RPC to get the ACL, but I'm seeing this fail on a publicly-viewable object I'm trying to work with, because its ACL isn't public.

The documentation of S3ObjectSummary.owner says:

/**
 * The owner of this object - can be null if the requester doesn't have
 * permission to view object ownership information
 */

S3Utils. getS3ObjectSummary should probably wrap that second RPC in a try/catch to leave owner as null in this case.