Change license to Apache 2.0 (#419)

Replace references to GNU Public License to Apache license in:

 - COPYING file
 - README
 - all source code below falco
 - rules files
 - rules and code below test directory
 - code below falco directory
 - entrypoint for docker containers (but not the Dockerfiles)

I didn't generally add copyright notices to all the examples files, as
they aren't core falco. If they did refer to the gpl I changed them to
apache.

examples/mitm-sh-installer/web_root/install-software.sh

@@ -1,21 +1,22 @@
 #!/bin/bash
 #
-# Copyright (C) 2013-2014 My Company inc.
+# Copyright (C) 2018 Draios Inc.
 #
-# This file is part of my-software
+# This file is part of falco.
 #
-# my-software is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License version 2 as
-# published by the Free Software Foundation.
+# 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
 #
-# my-software is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
+#     http://www.apache.org/licenses/LICENSE-2.0
 #
-# You should have received a copy of the GNU General Public License
-# along with my-software.  If not, see <http://www.gnu.org/licenses/>.
+# 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.
 #
+
 set -e
 
 function install_rpm {