Introduce JsonUnit and a bunch KV related functions to simplify itests.

[srgg]

Description

The PR introduces (JsonUnit)[https://github.com/lukas-krecan/JsonUnit] library which is used to make assertions.

Motivation and Context

Sometimes it is hard to read test tons of assertions in test cases, especially when it is required to check more or less complex objects. This PR demonstrates how Json may simplify testing and make test cases more human readable.

How Has This Been Tested?

The modified test is still green.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ x] My code follows the code style of this project.
• [ x] I have read the CONTRIBUTING document.
• [ x] I have added tests to cover my changes.
• [ x] All new and existing tests passed.
• [ x] Javadoc comments for any new public classes, interfaces, etc.
• A basho_docs PR for new or changed features (basho/basho_docs#???)

Pull requests that are small and limited in scope are most welcome.