Add basic support for CloudFoundry Redis

[quickjp2]

CloudFoundry automatically injects Redis info into apps via the VCAP_SERVICES environment variable. I've added code to use that env var when a user adds info about the service they chose and uses the name of the service as the Redis prefix.

I've added documentation for what env vars to set, as well as a test to check the call that uses the CF env vars.

I believe I've followed best practices, but if you notice something off, let me know and I can fix it. 😄

[joeyguerra]

What about changing the stagey a little bit to "push out the change impact" from the main function by changing the responsibility of getRedisEnv to actually building and returning the correctly formatted Redis URL.

const getRedisUrl = (robot) => {
/// do all the url building in here.
}

[joeyguerra]

Closing due to staleness.