Redis 6 Support

[seandstewart]

We seem to have a few failing tests with the introduction of Redis 6.0 into the pipeline. Unfortunately the current output is not very helpful:

https://github.com/aio-libs/aioredis/runs/1468097976?check_suite_focus=true#step:11:5000

[Andrew-Chen-Wang]

Just to get this fixed quickly, some things to take note:

• test_master__auth: add username as a keyword parameter next to password in conftest.py's start_server fixture. We may just need two different tests to make sure username and password are both checked.
• test_auth: the message is just different for Redis 6.0. You may want to test both the message for password and the one for username like aforementioned.
• test_failover_command : not entirely sure what's wrong
• test_client_list : Redis 6.2 added laddr. I'm not able to see that for myself, strangely enough... Set to MOCK.Any
• test_client_list__unixsocket: again, I couldn't see it, so I'm not sure what part of Redis instance could show this...
• test_command_info: it's just a Redis 6.0 addition

[seandstewart]

I'm going to remove Redis 6 from the pipeline until we've patched this so we can have a green build again on master.

[asvetlov]

I'm going to remove Redis 6 from the pipeline until we've patched this so we can have a green build again on master.

The best you can do now

[seandstewart]

This issue should be resolved as of #891.