Added extra unit tests

[shmuelk]

Description

Added extra tests for various APIs and error conditions that weren't tested. I also enabled some tests that were commented out due to Redis server version issues in the past. Lastly the Redis.info test now writes out the server version to the log.

Motivation and Context

Improve our test coverage

How Has This Been Tested?

Ran swift test on both Linux and macOS.

Checklist:

• [ ] I have submitted a CLA form
• [ ] If applicable, I have updated the documentation accordingly.
• [x] If applicable, I have added tests to cover my changes.

[youming-lin]

Looks good. Should all the tests have expectations, or just selected ones?

[shmuelk]

Just the ones that do. Eventually we need to go over the Kitura-redis tests and use the expectation paradigm all over the place.