Fix formatting of random testing seed

The whitespace is not aligned correctly and it might be crazy-making to
some developers.

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -120,7 +120,7 @@ class BuildPlugin implements Plugin<Project> {
                 println "  JDK Version           : ${gradleJavaVersionDetails}"
                 println "  JAVA_HOME             : ${gradleJavaHome}"
             }
-            println " Random Testing Seed    : ${project.testSeed}"
+            println "  Random Testing Seed   : ${project.testSeed}"
 
             // enforce gradle version
             GradleVersion minGradle = GradleVersion.version('3.3')