Add more debugging messages

[abravalheri]

Although errors and warnings are being logged, some times the strategies
result in empty sets of nodes. Being able to see more information in the
logs is helpful to troubleshoot complex cluster systems.

[beardedeagle]

Please fix conflcts @abravalheri

[abravalheri]

Hi @beardedeagle, thank you for the message. Before rushing to fix the conflicts, did you had the chance to have a quick look at the proposed changes? Do they make sense? I wonder if that is the best way to go, or something different would be the best (e.g. using the default Elixir logger, or relying on macros to eliminate overhead).

(Sorry this was submitted 1 year ago, and since I had no interactions from the maintainers I thought maybe the design of this change was inconsistent with their long-term vision)