Support for passing arbitrary command-line/configuration params to factories

[lovetoburnswhen]

What action do you want to perform

I would like to test with a password protected (--require-pass) instance factories.redis_proc

What are the results

tests/conftest.py:13: in <module>
    redis_server = factories.redis_proc(**redis_kwargs, logsdir='/tmp')
E   TypeError: redis_proc() got an unexpected keyword argument 'password'

What are the expected results

The kwargs to be passed on to redis-server

[fizyk]

https://redis.io/topics/config