Build: Enforce that gradle idea was run before importing in intellij

Due to how intellij imports gradle projects, the tasks which setup
resources are not run. This means we must be sure to run gradle idea
from the command line before importing into elasticsearch. This change
adds a simple marker file to indicate we have run from the command line
before importing. It won't help for new projects that add plugin
metadata, but it will at least make sure the initial project is set up
correctly.

build.gradle

@@ -169,6 +169,15 @@ idea {
     vcs = 'Git'
   }
 }
+// Make sure gradle idea was run before running anything in intellij (including import).
+File ideaMarker = new File(projectDir, '.local-idea-is-configured')
+tasks.idea.doLast {
+  ideaMarker.setText('', 'UTF-8')
+}
+if (System.getProperty('idea.active') != null && ideaMarker.exists() == false) {
+  throw new GradleException('You must run gradle idea from the root of elasticsearch before importing into IntelliJ')
+}
+
 
 // eclipse configuration
 allprojects {