Bug fixes

• Deleted cluster snapshots now clean up correctly: when a snapshot no longer exists in AWS, the AWS > Doc DB > DB Cluster Snapshot > CMDB control now removes it from the CMDB instead of going into an error state.
• AWS > Doc DB > DB Cluster Snapshot > Discovery no longer records public and shared snapshots owned by other AWS accounts. Previously these were recorded, and their CMDB controls then failed on every run.