ByteChannel can only read objects from buckets owned by accessing user

[ryan-williams]

• S3SeekableByteChannel constructor looks for bucket name in S3FileStore.getBucket
• S3FileStore.getBucket delegates to AmazonS3.listBucket, which only returns buckets owned by the current user.

The result is that you can't open a byte-channel for an object in a bucket not owned by the current user.

Arguably, the bug is in S3FileStore.getBucket, which IIUC should be able to see buckets that the current user can see, not just buckets that the current user owns.

[ejschoen]

For what it's worth, it can only write objects from buckets owned by the user, too.