Fix Java6BuiltInsWithJDKMembersTest

After update of the project to JDK 8, the default JDK at java.home is
now JDK 8. However, this test relied on the fact that the default is JDK
6. Pass the path to the JDK 6 explicitly

compiler/util/src/org/jetbrains/kotlin/utils/PathUtil.java

@@ -153,7 +153,12 @@ public class PathUtil {
 
     @NotNull
     public static List<File> getJdkClassesRoots() {
-        return JavaSdkUtil.getJdkClassesRoots(new File(System.getProperty("java.home")), true);
+        return getJdkClassesRoots(System.getProperty("java.home"));
+    }
+
+    @NotNull
+    public static List<File> getJdkClassesRoots(@NotNull String javaHome) {
+        return JavaSdkUtil.getJdkClassesRoots(new File(javaHome), true);
     }
 
     @NotNull