Pass serialization tests on AR 4.2

- Made testing of seriliazed_attributes with init_with only with AR less
  than 4.2 as 4.2 has added more stricter code to check the
  serialization mismatch when the object gets initialized.
- Made testing of raising exception while saving object with
  serialization mismatch only with AR less than 4.2.
- Added test case for testing raising exception while initializing new
  object with serialization mismatch when AR version is greater than or
  equal to 4.2.