Adapt to Redis ACLs

ca has been used the obsolete style of Redis configuration which shares one password between users. This mode is insecure. I've adapt the implementation to use the new ACL-based configuration (Redis has its own ACL file and ca's configuration file must contain the appropriate username too). This MR also updates the address in GitLab's URLs.

sentinel_ca/redis.py

@@ -40,6 +40,7 @@ def init_redis(conf):
     return redis.StrictRedis(
             host=conf.get("redis", "host"),
             port=conf.getint("redis", "port"),
+            username=conf.get("redis", "username"),
             password=conf.get("redis", "password"),
             unix_socket_path=redis_socket
     )