Support MinIO to be deployed on more than 32 nodes (#8492)

This PR implements locking from a global entity into
a more localized set level entity, allowing for locks
to be held only on the resources which are writing
to a collection of disks rather than a global level.

In this process this PR also removes the top-level
limit of 32 nodes to an unlimited number of nodes. This
is a precursor change before bring in bucket expansion.

pkg/dsync/dsync_private_test.go

@@ -0,0 +1,58 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// GOMAXPROCS=10 go test
+
+package dsync
+
+import "testing"
+
+// Tests dsync.New
+func TestNew(t *testing.T) {
+	nclnts := make([]NetLocker, 33)
+	if _, err := New(nclnts); err == nil {
+		t.Fatal("Should have failed")
+	}
+
+	nclnts = make([]NetLocker, 1)
+	if _, err := New(nclnts); err == nil {
+		t.Fatal("Should have failed")
+	}
+
+	nclnts = make([]NetLocker, 2)
+	nds, err := New(nclnts)
+	if err != nil {
+		t.Fatal("Should pass", err)
+	}
+
+	if nds.dquorumReads != 1 {
+		t.Fatalf("Unexpected read quorum values expected 1, got %d", nds.dquorumReads)
+	}
+
+	if nds.dquorum != 2 {
+		t.Fatalf("Unexpected quorum values expected 2, got %d", nds.dquorum)
+	}
+
+	nclnts = make([]NetLocker, 3)
+	nds, err = New(nclnts)
+	if err != nil {
+		t.Fatal("Should pass", err)
+	}
+
+	if nds.dquorumReads != nds.dquorum {
+		t.Fatalf("Unexpected quorum values for odd nodes we expect read %d and write %d quorum to be same", nds.dquorumReads, nds.dquorum)
+	}
+}