Redis proxy cleanup

Some cleanup of !3220 (merged)

• Redis connections: the client name was set twice

• test_redis_connections: take into account that the tango db could be accessing Redis

• Beacon connection: calling SafeRedisProxy.close on greenlet garbage collection makes no sense (it is a reusable proxy that is greenlet-safe). Only FixedConnectionRedisDbProxy.close makes sense (not greenlet-safe).

• Beacon connection: simplify proxy and connection pools with RedisProxyId (name, db, type). For each RedisProxyId we will have one reusable SafeRedisProxy and one Redis connection pool. We don't really need a different pool for a different name or type, but keep it for now.