Skipped serialization tests related to custom and bcrypt code for AR > 4.2

- These 2 tests were changed on Rails side in
  https://github.com/rails/rails/commit/24b6fa59523dc9eccf0a7c553d3da083ea860045
- The behavior is changed and they are not passing on Rails side also.
  So skipped them for AR > 4.2
Added the updated test case for serialized with coder for Rails 4.2

- The test was introduced in Rails in this commit https://github.com/rails/rails/commit/24b6fa59523dc9eccf0a7c553d3da083ea860045