fix(stakes): fix mining age reset function and add test

[drcpu-github]

1. Need to clone the by_rank iterator in reset_mining_age because position starts consuming it and you reset the wrong validators.
2. Add a test to prove correctness of the function. Also removed the filter in by_rank as it makes testing easier.
3. Fixed a bunch of other tests.
4. Changed the verbosity of the log function.