Remove serialization model shared examples

- Remove unused model to_json method
- Remove unused model class to_json method
- Remove unused model default_order_by
- Remove timestamps model shared examples
- Add rspec-its gem

[#72664052]

Signed-off-by: Joseph Palermo <jpalermo@pivotallabs.com>
Updating an AppSecurityGroup to a running or staging default is now a PUT

[#73760110]