Silence queue enumeration "normal" errors

[tequeter]

This Pull Request silences ipptool errors when the module tries to enumerate queues from a stopped CUPS service. See #251 for more info.

This is what I added/changed/removed and why I did it ...

1. I caught and redirected to the debug log the PuppetX::Cups::Ipp::QueryError when trying to enumerate classes and printers. Querying CUPS at this point cannot be guaranteed to succeed, but generates big noisy "normal" errors.
2. I updated the documentation accordingly.
3. I added an acceptance test for it. You can reproduce the issue easily by checking out the first commit.

Legal statement:

By committing to this project I transfer the full copyright for my contributions
to the current project maintainer as per the project's LICENSE file.

[leoarnold]

I can see where you are going with this, but silent fails have been and always will be a road to making troubleshooting unnecessarily hard and frustrating.

If you desire to have silent fails, please work with your own fork. For the general purpose, the underlying cause should be identified and dealt with.

[tequeter]

Hm, fair point.

What if I checked that I can connect to TCP localhost:631 before trying to call ipptool, instead?