Implement a custom HystrixPropertiesStrategy plugin

Add a custom HystrixPropertiesStrategy implementation where getCommandPropertiesCacheKey is overridden to return null so that HystrixPropertiesFactory will always generate a new HystrixCommandProperties for each new HystrixCommand instantiation.
> A cacheKey should be faster to produce than the actual object to be cached

Agreed. To assess whether it was worth the effort (maybe this is where we should do more microbenchmarking ? ;) ), but I did a quick trace through the code needed to produce a fresh properties object it did *not* look cheap and felt that Jackson reflection-based to-JSON to get a cachekey might be faster than doing that. 

Please take a look and let me know what you think.