Refactor JDK lookup in third_party

Change-Id: Iafec2bccb8892f5cd7877227a9f357b45084fe55
diff --git a/tools/create_r8lib.py b/tools/create_r8lib.py
index 1c349e1..37bea93 100755
--- a/tools/create_r8lib.py
+++ b/tools/create_r8lib.py
@@ -134,7 +134,7 @@
     cmd.extend(['--pg-conf-output', args.output + '.config'])
     cmd.extend(['--pg-map-output', args.output + '.map'])
     cmd.extend(['--partition-map-output', args.output + '_map.zip'])
-    cmd.extend(['--lib', jdk.GetJdkHome()])
+    cmd.extend(['--lib', jdk.GetDefaultJdkHome()])
     if args.pg_conf:
         for pgconf in args.pg_conf:
             cmd.extend(['--pg-conf', pgconf])