S3 extension misuses AWS SDK to get content size

[zyga]

Getting the content size should not happen with s3Object.getObjectMetadata as that is too late, and we're already GETting the whole blob needlessly.

From my local patch:

+        var req = new GetObjectMetadataRequest(s3Properties.getBucketName(), key);
+        var objMeta = amazonS3.getObjectMetadata(req);

This way we can get the meta-data in a simple HEAD request, which is not wasting bandwidth.