Kill server and proxy via SIGQUIT in ssl-opt.sh

SIGKILL interferes with memory checking in valgrind.
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 4afc527..8f64e54 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -449,7 +449,7 @@
         kill $SRV_PID
         sleep 0.01
         if kill -0 $SRV_PID >/dev/null 2>&1; then
-            kill -KILL $SRV_PID
+            kill -3 $SRV_PID
             wait $SRV_PID
         fi
 
@@ -457,7 +457,7 @@
             kill $PXY_PID >/dev/null 2>&1
             sleep 0.01
             if kill -0 $PXY_PID >/dev/null 2>&1; then
-                kill -KILL $PXY_PID
+                kill -3 $PXY_PID
                 wait $PXY_PID
             fi
         fi