Add missing license check files.

Forgot to add these on the last commit.

Original commit: elastic/x-pack-elasticsearch@4d205e191d

dev-tools/elasticsearch_license_header.txt

@@ -0,0 +1,14 @@
+ELASTICSEARCH CONFIDENTIAL
+__________________
+
+ [2014] Elasticsearch Incorporated. All Rights Reserved.
+
+NOTICE:  All information contained herein is, and remains
+the property of Elasticsearch Incorporated and its suppliers,
+if any.  The intellectual and technical concepts contained
+herein are proprietary to Elasticsearch Incorporated
+and its suppliers and may be covered by U.S. and Foreign Patents,
+patents in process, and are protected by trade secret or copyright law.
+Dissemination of this information or reproduction of this material
+is strictly forbidden unless prior written permission is obtained
+from Elasticsearch Incorporated.

dev-tools/license_header_definition.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<additionalHeaders>
+    <javadoc_style>
+        <firstLine>/*</firstLine>
+        <beforeEachLine> * </beforeEachLine>
+        <endLine> */EOL</endLine>
+        <!--skipLine></skipLine-->
+        <firstLineDetectionPattern>(\s|\t)*/\*.*$</firstLineDetectionPattern>
+        <lastLineDetectionPattern>.*\*/(\s|\t)*$</lastLineDetectionPattern>
+        <allowBlankLines>false</allowBlankLines>
+        <isMultiline>true</isMultiline>
+    </javadoc_style>
+</additionalHeaders>

dev-tools/pmd/custom.xml

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+<?xml version="1.0"?>
+<ruleset name="Custom ruleset"
+    xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 http://pmd.sourceforge.net/ruleset_2_0_0.xsd">
+  <description>
+  Default ruleset for elasticsearch server project
+  </description>
+  <rule ref="rulesets/java/basic.xml"/>
+  <rule ref="rulesets/java/braces.xml"/>
+  <rule ref="rulesets/java/clone.xml"/>
+  <rule ref="rulesets/java/codesize.xml"/>
+  <rule ref="rulesets/java/coupling.xml">
+     <exclude name="LawOfDemeter" />
+  </rule>
+  <rule ref="rulesets/java/design.xml"/>
+  <rule ref="rulesets/java/unnecessary.xml">
+     <exclude name="UselessParentheses" />
+  </rule>
+</ruleset>