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/xl-v1-utils_test.go

@@ -125,7 +125,7 @@ func TestHashOrder(t *testing.T) {
 	for i, testCase := range testCases {
 		hashedOrder := hashOrder(testCase.objectName, 16)
 		if !reflect.DeepEqual(testCase.hashedOrder, hashedOrder) {
-			t.Errorf("Test case %d: Expected \"%#v\" but failed \"%#v\"", i+1, testCase.hashedOrder, hashedOrder)
+			t.Errorf("Test case %d: Expected \"%v\" but failed \"%v\"", i+1, testCase.hashedOrder, hashedOrder)
 		}
 	}
 
@@ -133,6 +133,10 @@ func TestHashOrder(t *testing.T) {
 	if hashedOrder := hashOrder("This will fail", -1); hashedOrder != nil {
 		t.Errorf("Test: Expect \"nil\" but failed \"%#v\"", hashedOrder)
 	}
+
+	if hashedOrder := hashOrder("This will fail", 0); hashedOrder != nil {
+		t.Errorf("Test: Expect \"nil\" but failed \"%#v\"", hashedOrder)
+	}
 }
 
 // newTestXLMetaV1 - initializes new xlMetaV1, adds version, allocates a fresh erasure info and metadata.