Convert gateways into respective packages (#5200)

- Make azure gateway a package
- Make b2 gateway a package
- Make gcs gateway a package
- Make s3 gateway a package
- Make sia gateway a package

cmd/gateway/sia/gateway-sia_test.go

@@ -0,0 +1,32 @@
+/*
+ * Minio Cloud Storage, (C) 2017 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.
+ */
+
+package sia
+
+import (
+	"testing"
+)
+
+func TestSianon2xx(t *testing.T) {
+	for i := 0; i < 1000; i++ {
+		actual := non2xx(i)
+		expected := i < 200 || i > 299
+
+		if actual != expected {
+			t.Errorf("Test case %d: non2xx(%d) returned %t but expected %t", i+1, i, actual, expected)
+		}
+	}
+}