Create new Redis connection when REDIS_URI changes

When the REDIS_URI configuration setting is changed, the Redis client should be reconfigured with a new connection pool, just like we do with the database.

It appears redis-py manages the connection pool by itself and doesn't expose ways to explicitely destroy it or close all connections (this is done automatically when all connections loose scope).

This fix ensures that the unit tests don't accidentally work on the Redis database configured in MUTALYZER_SETTINGS, which was quite an unfortunate bug.