Add elasticache redis

This adds a new Service collector called Elasticache Redis (ECR) to deal with the cloudwatch statistics that are available for the Redis version of Elasticache.  The metrics are different then the memcached Elasticache implementation, and currently Redis instances show up on the NR platform, but don't show many metrics, because they don't exist for Redis.  This code treats Redis as a completely different service (although it is not), but that seemed like the cleanest way to get the metrics collected since it didn't look like NR Platform GUI supported two different kinds of things under one service.  This is the work for the collector side and it would have to be configured on the Platform side, which somebody else would have to do.