Add support/config for ioredis Parse "Cache Adapter"

[BobDickinson]

https://github.com/ParsePlatform/parse-server/wiki/Configuring-Cache-Adapters

In our implementation we need a Parse Cache Adapter that supports sentinal configuration (for Redis failover). This means we need to use the "ioredis" module with sentinel support/config (not the standard "redis" module). We also need to support dynamic reconfig when Redis service availability (Sentinel set) changes. Ideally we would do this by querying Consul to configure the ioredis connection, and use a SIGHUP handler to reconfigure, as we do in Synchro.

The alternate (ugly) way to do this is the just have the Parse API server connect to the Redis master, and then when ContainerPilot detects a master change, restart the Parse API service/container.