[#702] Improve mirroring summary

[Adnilson]

Description

This PR was created to make easier the implementation of the previous one as there were many conflicts by merging the debian changes that refactored the classes used by the implementation of this feature.

These are the changes I did on my technical interview to improve the summary of the mirroring process.

Fixes https://github.com/SUSE/rmt/issues/702

Other Notes

Maybe we can update some rubocop rules

Regarding spec/lib/rmt/cli/mirror_spec.rb:

• RSpec/ExpectOutput: Use expect { ... }.to output(...).to_stdout instead of mutating $stdout.

  I was unable to test well the summary output with the output helper, so I decided to use the $stdout which makes our test more robust.

• RSpec/MultipleExpectations and RSpec/ExampleLength were ignored because of the changes belonging to the summary output which have more information.

RSpec/ClassLength in this case there 3 more lines than the limit which is 177. Is there a reason for this number? I prefer deep modules (with a simple interface) than shallow modules (with a complex interface) as I learned from: A Philosophy of Software Design by John Ousterhout.

[Adnilson]

LGTM, but please merge after rmt 2.16 is released

How should I update package/obs/rmt-server.changes?

[Adnilson]

LGTM, but please merge after rmt 2.16 is released

How should I update package/obs/rmt-server.changes?

Just merged master and updated the release to version 2.17