Also add endswith to lua parser (#443)

* Also add endswith to lua parser

Add endswith as a symbol so it can be parsed in filter expressions.

* Unit test for endswith support

Add a test case for endswith support, based on the filename ending with null.

test/rules/endswith.yaml

@@ -0,0 +1,22 @@
+#
+# Copyright (C) 2016-2018 Draios Inc dba Sysdig.
+#
+# This file is part of falco.
+#
+# 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.
+#
+- rule: open_ending with null
+  desc: A file ending with null is opened
+  condition: evt.type=open and fd.name endswith null
+  output: "An open was seen (command=%proc.cmdline)"
+  priority: WARNING