More specific error when parent image/base image truly doesn't exist in registry

[ben-alkov]

• CLOUDBLD-7086

Signed-off-by: Ben Alkov [email protected]# Maintainers will complete the following section

• [ ] Commit messages are descriptive enough
• [ ] Code coverage from testing does not decrease and new code is covered
• [ ] Python type annotations added to new code
• [ ] JSON/YAML configuration changes are updated in the relevant schema
• [ ] Changes to metadata also update the documentation for the metadata
• [ ] Pull request has a link to an osbs-docs PR for user documentation updates
• [ ] New feature can be disabled from a configuration file