Fix ART buildbots to use jdk8 prebuilts

Test: Manual
Bug: 63902894
Change-Id: I139e613df6efcabd5ca667d6d569cc7577e57355
diff --git a/tools/run-jdwp-tests.sh b/tools/run-jdwp-tests.sh
index 225fb39..17c84b4 100755
--- a/tools/run-jdwp-tests.sh
+++ b/tools/run-jdwp-tests.sh
@@ -19,6 +19,11 @@
   exit 1
 fi
 
+if [ -z "$ANDROID_JAVA_TOOLCHAIN" ] ; then
+  source build/envsetup.sh
+  setpaths # include platform prebuilt java, javac, etc in $PATH.
+fi
+
 if [ -z "$ANDROID_HOST_OUT" ] ; then
   ANDROID_HOST_OUT=${OUT_DIR-$ANDROID_BUILD_TOP/out}/host/linux-x86
 fi