Duplicate Dockerfile in the build directory (#204)

* Duplicate Dockerfile in the build directory

Signed-off-by: Anatoliy Bazko <abazko@redhat.com>

build/Dockerfile

@@ -0,0 +1,13 @@
+# Copyright (c) 2018-2020 Red Hat, Inc.
+# This program and the accompanying materials are made
+# available under the terms of the Eclipse Public License 2.0
+# which is available at https://www.eclipse.org/legal/epl-2.0/
+#
+# SPDX-License-Identifier: EPL-2.0
+#
+# Contributors:
+#   Red Hat, Inc. - initial API and implementation
+#
+
+# Empty file.
+# Is required by operator-sdk for some tasks.