Google App Engine(GAE) : Rolling back previous incomplete deployment(running appcfg roolback)

While deploying Google App Engine web app you may face:
"GAE appcfg rollback not working: 409 Conflict Another transaction by user is already in progress for app".
To fix this got to APP_ENGINE_SDK_DIRECTORY/bin where the appcfg.sh is located:
Run this command there:
sh appcfg.sh rollback GAE_APP_DIR/
where GAE_APP_DIR: your project directory where the WEB_INF foler is located example:
sh appcfg.sh rollback GAE_APP_DIR/web/