This is a sub-issue of #1910624: [META] Introduce and complete configuration schemas in all of core.
Problem/motivation
#1866610: Introduce Kwalify-inspired schema format for configuration introduced some config schema coverage for user module, but it is not complete. The changelog leads to (hopefully extensive) documentation on the format at http://drupal.org/node/1905070. While there are little cleanups planned for the format overall, the current format is a result of months of back and forths, so it should be perfectly fine to apply it more widely to core.
Proposed solution
Figure out the missing pieces that are not yet covered. Write schema file sections for them. Clean up / fix any issues in current schema.
Schema in place
user.mail.yml
user.settings.yml
Schema not yet in place
user.flood.yml
user roles