Don't error if stopping mysql fails in CI

And mask mysql to prevent it from being started

Author: ChrisDenton

src/ci/scripts/free-disk-space.sh

@@ -152,7 +152,8 @@ execAndMeasureSpaceChange() {
 # REF: https://github.com/apache/flink/blob/master/tools/azure-pipelines/free_disk_space.sh
 cleanPackages() {
     # Stop services to avoid issues when removing their packages.
-    sudo systemctl stop mysql
+    sudo systemctl stop mysql || echo "::warning::The command [sudo systemctl stop mysql] failed"
+    sudo systemctl mask mysql || echo "::warning::The command [sudo systemctl mask mysql] failed"
 
     local packages=(
         '^aspnetcore-.*'