ART: Fix for pkill on device in run-jdwp-tests.sh

Adds workaround to run-jdwp-tests.sh for pkill on old devices running
within the ART buildbots.

Test: manual
Bug: 28877702
Change-Id: I419165fd9f254dae4db94a0e7fffb66feed22360
diff --git a/tools/run-jdwp-tests.sh b/tools/run-jdwp-tests.sh
index d376cad..eebc092 100755
--- a/tools/run-jdwp-tests.sh
+++ b/tools/run-jdwp-tests.sh
@@ -360,7 +360,9 @@
 if [[ $mode == "host" ]]; then
   pkill -9 -f /bin/dalvikvm
 else
-  adb shell pkill -9 -f /bin/dalvikvm
+  # Tests may run on older Android versions where pkill requires "-l SIGNAL"
+  # rather than "-SIGNAL".
+  adb shell pkill -l 9 -f /bin/dalvikvm
 fi
 echo "Done."