Add unix socket tests to CI

[WisdomPill]

CI is missing unix socket tests

[WisdomPill]

@terencehonles I guess we could add another instance of redis in start_redis.sh script to start an instance using unix sockets.

Am I right?

In case, I would be glad to take on the issue

[terencehonles]

No, I actually had fixed this with #506 and now we don't use a service definition and do the same thing as the test README suggests.

[terencehonles]

Thanks for making sure this didn't get dropped!