CLI-1370: PHP warning in pull:db when backup fails

[danepowell]

Motivation

Fixes warnings when a backup (or any other Cloud API task) fails

Proposed changes

Check the notification response to make sure the task completed successfully

Testing steps

1. Follow the contribution guide to set up your development environment or download a pre-built acli.phar for this PR.
2. Clear the kernel cache to pick up new and changed commands: ./bin/acli ckc
3. (add specific steps for this pr)