Test: Fix integ test extra config files to work with more than one

Groovy does some crazy capturing when using closures inside a loop. In
this case, it somehow decided the local loop variable would be
modified, and so each closure was getting a wrapped value that would be
updated on each loop iteration, until all the closures pointed at the
last value. This change fixes the loop to extract the object to be used by
the closures.

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

@@ -291,9 +291,10 @@ class ClusterFormationTasks {
         File configDir = new File(node.homeDir, 'config')
         copyConfig.into(configDir) // 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()) {
+            Object extraConfigFileValue = extraConfigFile.getValue()
             copyConfig.doFirst {
                 // make sure the copy won't be a no-op or act on a directory
-                File srcConfigFile = project.file(extraConfigFile.getValue())
+                File srcConfigFile = project.file(extraConfigFileValue)
                 if (srcConfigFile.isDirectory()) {
                     throw new GradleException("Source for extraConfigFile must be a file: ${srcConfigFile}")
                 }
@@ -303,7 +304,7 @@ class ClusterFormationTasks {
             }
             File destConfigFile = new File(node.homeDir, 'config/' + extraConfigFile.getKey())
             // wrap source file in closure to delay resolution to execution time
-            copyConfig.from({ extraConfigFile.getValue() }) {
+            copyConfig.from({ extraConfigFileValue }) {
                 // this must be in a closure so it is only applied to the single file specified in from above
                 into(configDir.toPath().relativize(destConfigFile.canonicalFile.parentFile.toPath()).toFile())
                 rename { destConfigFile.name }