Moving away from goamz to use minio-go instead. (#4193)

minio-go does fully managed way of handling S3 API requests

  - Automatic bucket location management across all s3 regions.
  - Transparently upload large files in multipart if file 64MB
    or larger.
  - Right GetObject() API provides compatibility with
    io.ReadWriteSeeker interface.
  - Various other APIs including bulk deletes, server side object
    copy, bucket policies and bucket notifications.

Fixes #4182

glide.yaml

@@ -63,3 +63,5 @@ import:
 - package: github.com/segmentio/analytics-go
   version: 2.1.1
 - package: github.com/rsc/letsencrypt
+- package: github.com/minio/minio-go
+  version: ^2.0.2