Fix bundling behavior when files/globs in zapp.yaml do not have a match

Fixes https://github.com/zerovm/zpm/issues/119.

This change does two things:

- If a glob in the zapp.yaml "bundling" or "ui" doesn't match any files, log a WARNING
- If none of the globs in "bundling" and "ui" match anything, raise an exception; this means the globs are wrong and there won't be anything useful in the zapp tar file