Add Expiry Property to allow log containers to expire

[SidBala]

var redisTransport  = new Redis({
    length: 5000,
    container: 'logsContainer',
    level: 'info',
    expire: 7 * 24 * 60 * 60 // Expire in a week's time.
})

[yads]

Looks good, how about updating the README to go along with this change?

[yads]

@SidBala I've added your code around not messing with a provided redis client to master