Provide more meaningful error messages when the kit push command fails

[brett-hodges]

Describe the problem you're trying to solve
Please refer to Closed Issue #393

kit push returns an ambiguous error message when the command fails because a Registry doesn't support Repository names with multiple-levels beyond what is expected.

For example, the current error message use case mentioned above is:

Pushing jozu.ml/jozu-test/repo-level-testing/mymodel:latest
Failed to push: failed to copy to remote: Not Found (additional info: {"status":404,"error":"Not Found"})

Describe the solution you'd like
The error message should clearly specify that the issue is with multi-level Repository name.
For example, consider:
Failed to push: failed to copy to remote registry: Multi-level repository names are not supported at this time.