8080275: transparently download testng.jar for Nashorn testing

Instead of asking the user to manually download and install testng.jar, automate the process via "ant externals".

Reviewed-by: hannesw, sundar
diff --git a/nashorn/make/project.properties b/nashorn/make/project.properties
index 35e1af9..aab32c6 100644
--- a/nashorn/make/project.properties
+++ b/nashorn/make/project.properties
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2010, 2014, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2010, 2015, Oracle and/or its affiliates. All rights reserved.
 # DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 #
 # This code is free software; you can redistribute it and/or modify it
@@ -77,8 +77,11 @@
 # configuration for java flight recorder
 run.test.jvmargs.jfr=-XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:FlightRecorderOptions=defaultrecording=true,disk=true,dumponexit=true,dumponexitpath=${build.dir},stackdepth=128
 
+# test library location
+test.lib=${basedir}${file.separator}test${file.separator}lib
+
 # jars refererred
-file.reference.testng.jar=test/lib/testng.jar
+file.reference.testng.jar=${test.lib}${file.separator}testng.jar
 
 # Set testng verbose level
 # From TestNG docs: "the verbosity level (0 to 10 where 10 is most detailed)
@@ -243,9 +246,9 @@
     -fx \
     ${test.script.dir}${file.separator}jfx.js
 
-file.reference.jemmyfx.jar=test${file.separator}lib${file.separator}JemmyFX.jar
-file.reference.jemmycore.jar=test${file.separator}lib${file.separator}JemmyCore.jar
-file.reference.jemmyawtinput.jar=test${file.separator}lib${file.separator}JemmyAWTInput.jar
+file.reference.jemmyfx.jar=${test.lib}${file.separator}JemmyFX.jar
+file.reference.jemmycore.jar=${test.lib}${file.separator}JemmyCore.jar
+file.reference.jemmyawtinput.jar=${test.lib}${file.separator}JemmyAWTInput.jar
 file.reference.jfxrt.jar=${java.home}${file.separator}lib${file.separator}ext${file.separator}jfxrt.jar
 testjfx.run.test.classpath=\
     ${file.reference.jemmyfx.jar}${path.separator}\