mavsdk_tests: fix wait script output

test/mavsdk_tests/waitforgz.sh

@@ -1,7 +1,5 @@
 #!/usr/bin/env bash
 
 while gz stats -d 0 2>&1 | grep "An instance of Gazebo is not running."; do
-    echo "Still running"
+    echo "Gazebo not running yet ..."
 done
-
-echo "done"