Build: Make rest-spec-api a project so eclipse build works

The change makes rest-spec-api a project in the same way as we build dev-tools. it packages the tests and api in a bundle using the maven-remote-resources-plugin and uses the same plugin in the plugins and core pom to unpack the rest-api-spec into the target directory and references the rest tests there in the test resources.

The main stimulus for this change is that for those using Eclipse the current build does not work. After running `mvn eclipse:eclipse` the Eclipse IDE errors because the rest-api-spec is outside of the project scope, meaning that every time the command is run (required whenever any dependencies change), the class path of all the projects has to be manually fixed.

core/pom.xml

@@ -281,7 +281,7 @@
                 </includes>
             </testResource>
             <testResource>
-                <directory>${project.basedir}/../rest-api-spec</directory>
+                <directory>${elasticsearch.tools.directory}/rest-api-spec</directory>
                 <targetPath>rest-api-spec</targetPath>
                 <includes>
                     <include>api/*.json</include>

plugins/pom.xml

@@ -110,7 +110,7 @@
             <!-- REST API specifications copied from main Elasticsearch specs
                  because they are required to execute the REST tests in plugins  -->
             <testResource>
-                <directory>${project.basedir}/../../rest-api-spec</directory>
+                <directory>${elasticsearch.tools.directory}/rest-api-spec</directory>
                 <targetPath>rest-api-spec</targetPath>
                 <includes>
                     <!-- required by the test framework -->

pom.xml

@@ -708,6 +708,7 @@
                     <configuration>
                         <resourceBundles>
                             <resourceBundle>org.elasticsearch:dev-tools:${elasticsearch.version}</resourceBundle>
+                            <resourceBundle>org.elasticsearch:rest-api-spec:${elasticsearch.version}</resourceBundle>
                         </resourceBundles>
                         <outputDirectory>${elasticsearch.tools.directory}</outputDirectory>
                         <!-- don't include dev-tools in artifacts -->
@@ -1457,6 +1458,7 @@ org.eclipse.jdt.ui.text.custom_code_templates=<?xml version\="1.0" encoding\="UT
     </profiles>
     <modules>
         <module>dev-tools</module>
+        <module>rest-api-spec</module>
         <module>plugins</module>
         <module>core</module>
     </modules>

rest-api-spec/pom.xml

@@ -0,0 +1,37 @@
+<project>
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>org.elasticsearch</groupId>
+  <artifactId>rest-api-spec</artifactId>
+  <version>2.0.0-SNAPSHOT</version>
+  <name>Elasticsearch Rest API Spec</name>
+  <parent>
+      <groupId>org.sonatype.oss</groupId>
+      <artifactId>oss-parent</artifactId>
+      <version>7</version>
+      <relativePath></relativePath>
+  </parent>
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-remote-resources-plugin</artifactId>
+        <version>1.5</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>bundle</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <includes>
+            <include>**/*</include>
+          </includes>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>