[cbbs] Manually renaming/removing archive on filesystem provides inadequate information in UI.

Description:

Upon manual deletion/removal of an archive, the user is presented with the following error upon clicking on the backup archive in the UI:

Could not get repository information: could info repository repository. exit status 1

This error message does not inform the user why it could not get the repository information. The user may not be aware where the exit code comes from and what it means.

Steps to reproduce:

1. Create a repository with the archive name 'my_archive', repository name 'my_repo' and plan '_hourly_backups' using the backup service UI.
2. Delete or Rename 'my_archive' from the file system manually.
3. Click on repository 'my_repo' in the UI.

Expected behaviour:

The user is warned that the archive has been lost instead perhaps indicating why the backup service can't access the repository information.

The origin of the exit code is exposed to the user as coming from 'cbbackupmgr info' or the exit code is completely omitted.

Could not get repository information: The repository 'my_repo' has been lost, could not find 'my_archive' on the filesystem.

cbbackupmgr info returned with exit code 1.

What actually happens:

The user is presented with this warning instead:

Could not get repository information: could info repository repository. exit status 1