Update unit test for BCrypt password strategy

* Move specs into a more logical directory
* Remove subject/before/let statements
* Extract common code into scoped methods
Unused method argument - `args`. If it's necessary, use `_` or `_args` as an argument name to indicate that it won't be used. You can also write as `before_validation(*)` if you want the method to accept any arguments but don't care about them.