With CoreDNS now supporting etcdv3 as the DNS backend, we
can update our federation target to etcdv3. Users will now be
able to use etcdv3 server as the federation backbone.
Minio will update bucket data to etcdv3 and CoreDNS can pick
that data up and serve it as bucket style DNS path.
This patch modifies multipart upload related functions as below
* New multipart upload call creates file
EXPORT_DIR/.minio/BUCKET/PATH/TO/OBJECT/UPLOAD_ID.uploadid
* Put object part call creates file
EXPORT_DIR/.minio/BUCKET/PATH/TO/OBJECT/UPLOAD_ID.PART_NUMBER.MD5SUM_STRING
* Abort multipart call removes all files matching
EXPORT_DIR/.minio/BUCKET/PATH/TO/OBJECT/UPLOAD_ID.*
* Complete multipart call does
1. creates a staging file
EXPORT_DIR/.minio/BUCKET/PATH/TO/OBJECT/UPLOAD_ID.complete.TEMP_NAME
then renames to
EXPORT_DIR/.minio/BUCKET/PATH/TO/OBJECT/UPLOAD_ID.complete
2. rename staging file
EXPORT_DIR/.minio/BUCKET/PATH/TO/OBJECT/UPLOAD_ID.complete
to EXPORT_DIR/BUCKET/PATH/TO/OBJECT