kill gdbserver on device before start gdb test.

BUG=None
TEST=the process of gdbserver leader-exit.exp is gone.

Change-Id: Ifd7d47a7064275a16e1faf7faf03e6c1d281ff59
Reviewed-on: https://gerrit-int.chromium.org/37310
Commit-Queue: Yunlian Jiang <yunlian@google.com>
Reviewed-by: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
diff --git a/dejagnu/boards/gdbserver.sh.in b/dejagnu/boards/gdbserver.sh.in
index c1c048b..b74c685 100644
--- a/dejagnu/boards/gdbserver.sh.in
+++ b/dejagnu/boards/gdbserver.sh.in
@@ -8,5 +8,5 @@
 
 echo "Executing: ssh  ${RSA_FILE} ${REMOTE_SSH_FLAGS} root@${FLAGS_remote} \"${ssh_cmd}\"" >&2
 
-ssh ${REMOTE_SSH_FLAGS} root@${FLAGS_remote} "${ssh_cmd}"
+ssh ${REMOTE_SSH_FLAGS} root@${FLAGS_remote} "killall -9 gdbserver; ${ssh_cmd}"