Build: Add ability to specify extra configuration files for integ test

This change allows copy extra files into the integ test cluster before
it runs. However, it explicitly forbids overwriting elasticsearch.yml,
since that is generated.

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterConfiguration.groovy

@@ -18,6 +18,7 @@
  */
 package org.elasticsearch.gradle.test
 
+import org.gradle.api.GradleException
 import org.gradle.api.Project
 import org.gradle.api.file.FileCollection
 import org.gradle.api.tasks.Input
@@ -65,6 +66,9 @@ class ClusterConfiguration {
 
     Map<String, String> settings = new HashMap<>()
 
+    // map from destination path, to source file
+    Map<String, Object> extraConfigFiles = new HashMap<>()
+
     LinkedHashMap<String, Object> plugins = new LinkedHashMap<>()
 
     LinkedHashMap<String, Object[]> setupCommands = new LinkedHashMap<>()
@@ -93,4 +97,16 @@ class ClusterConfiguration {
     void setupCommand(String name, Object... args) {
         setupCommands.put(name, args)
     }
+
+    /**
+     * Add an extra configuration file. The path is relative to the config dir, and the sourceFile
+     * is anything accepted by project.file()
+     */
+    @Input
+    void extraConfigFile(String path, Object sourceFile) {
+        if (path == 'elasticsearch.yml') {
+            throw new GradleException('Overwriting elasticsearch.yml is not allowed, add additional settings using cluster { setting "foo", "bar" }')
+        }
+        extraConfigFiles.put(path, sourceFile)
+    }
 }

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy

@@ -167,7 +167,14 @@ class ClusterFormationTasks {
             'repositories.url.allowed_urls'   : 'http://snapshot.test*'
         ]
 
-        return project.tasks.create(name: name, type: DefaultTask, dependsOn: setup) << {
+        Copy copyConfig = project.tasks.create(name: name, type: Copy, dependsOn: setup)
+        copyConfig.into(new File(node.homeDir, 'config')) // copy must always have a general dest dir, even though we don't use it
+        for (Map.Entry<String,Object> extraConfigFile : node.config.extraConfigFiles.entrySet()) {
+            copyConfig.from(extraConfigFile.getValue())
+                      .into(new File(node.homeDir, 'config/' + extraConfigFile.getKey()))
+        }
+        copyConfig.doLast {
+            // write elasticsearch.yml last, it cannot be overriden
             File configFile = new File(node.homeDir, 'config/elasticsearch.yml')
             logger.info("Configuring ${configFile}")
             configFile.setText(esConfig.collect { key, value -> "${key}: ${value}" }.join('\n'), 'UTF-8')