Make Pirant compatible for multiple python versions

[aayush26]

Problem statement: Seems like pirant is compatible to only py2.7 currently. We should make it compatible for 3.4 and above also.
Solution suggested: @AmiraliM suggested on using SIX package
Scope of implementation: Fix existing codebase to make it compatible for all python versions.

References:
SIX package: https://pythonhosted.org/six/

[Cogitri]

Sorry, but doesn't pirant already work with python >=3? At least all tests pass here with python 3.6

[aayush26]

@Cogitri We need to recheck once again.
@AmiraliM found out an instance were it fails.
In python 3, response.context returns bytes while in python 2.7, it returns string. Hence, json.loads() works in 2.7 but not in 3.4
Why this was not captured in tests because we only wrote Unit tests and all these external responses using request library are mocked, hence we missed it and all tests passed.

[aayush26]

@AmiraliM , @Cogitri mentioned about using future over six. He also provided a reference: http://python-future.org/faq.html#what-is-the-relationship-between-future-and-six
Have a look into it and lets discuss how to resolve this issue or whether its already resolved by @Cogitri commit #18