Add large bucket support for erasure coded backend (#5160)

This PR implements an object layer which
combines input erasure sets of XL layers
into a unified namespace.

This object layer extends the existing
erasure coded implementation, it is assumed
in this design that providing > 16 disks is
a static configuration as well i.e if you started
the setup with 32 disks with 4 sets 8 disks per
pack then you would need to provide 4 sets always.

Some design details and restrictions:

- Objects are distributed using consistent ordering
  to a unique erasure coded layer.
- Each pack has its own dsync so locks are synchronized
  properly at pack (erasure layer).
- Each pack still has a maximum of 16 disks
  requirement, you can start with multiple
  such sets statically.
- Static sets set of disks and cannot be
  changed, there is no elastic expansion allowed.
- Static sets set of disks and cannot be
  changed, there is no elastic removal allowed.
- ListObjects() across sets can be noticeably
  slower since List happens on all servers,
  and is merged at this sets layer.

Fixes #5465
Fixes #5464
Fixes #5461
Fixes #5460
Fixes #5459
Fixes #5458
Fixes #5460
Fixes #5488
Fixes #5489
Fixes #5497
Fixes #5496

cmd/admin-handlers.go

@@ -52,14 +52,15 @@ const (
 var (
 	// This struct literal represents the Admin API version that
 	// the server uses.
-	adminAPIVersionInfo = madmin.AdminAPIVersionInfo{"1"}
+	adminAPIVersionInfo = madmin.AdminAPIVersionInfo{
+		Version: "1",
+	}
 )
 
 // VersionHandler - GET /minio/admin/version
 // -----------
 // Returns Administration API version
 func (a adminAPIHandlers) VersionHandler(w http.ResponseWriter, r *http.Request) {
-
 	adminAPIErr := checkAdminRequestAuthType(r, globalServerConfig.GetRegion())
 	if adminAPIErr != ErrNone {
 		writeErrorResponse(w, adminAPIErr, r.URL)
@@ -555,7 +556,6 @@ func (a adminAPIHandlers) HealHandler(w http.ResponseWriter, r *http.Request) {
 			writeSuccessResponseJSON(w, respBytes)
 		}
 	}
-	return
 }
 
 // GetConfigHandler - GET /minio/admin/v1/config