use echo to test whether host is up (#16322)

testing/fuchsia/run_tests.sh

@@ -33,14 +33,17 @@ trap reboot EXIT
 
 ./fuchsia_ctl -d $device_name pave  -i $1
 
-# TODO(gw280): Enable tests using JIT runner
 for i in {1..10}; do
-  ./fuchsia_ctl -d $device_name test \
-      -f flutter_aot_runner-0.far    \
-      -f flutter_runner_tests-0.far  \
-      -t flutter_runner_tests && break || sleep 15;
+  ./fuchsia_ctl -d $device_name ssh -c "echo up" && break || sleep 15;
 done
 
+# TODO(gw280): Enable tests using JIT runner
+
+./fuchsia_ctl -d $device_name test \
+    -f flutter_aot_runner-0.far    \
+    -f flutter_runner_tests-0.far  \
+    -t flutter_runner_tests
+
 ./fuchsia_ctl -d $device_name test \
     -f fml_tests-0.far  \
     -t fml_tests