Add a basic set of KorvClient tests

[tryexceptpass]

Using pytest as the test framework, add the basic tests that verify a client instance:

• Instantiate KorvClient connecting to a local server without errors using newly generated SSH keys.
• GET responses complete with the proper callback.
• STORE responses complete with the proper callback and with no callback.
• UPDATE responses complete with the proper callback and with no callback.
• DELETE responses complete with the proper callback and with no callback.
• Connection fails with the incorrect host address or port.
• Connection fails with the incorrect SSH key.