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.
I see, as neither `HystrixCommandProperties` nor its `Setter` has a clean toString method, forced to use reflection... 

A cacheKey should be faster to produce than the actual object to be cached, so I think that defaulting to null is not that bad actually (and will avoid the ever-growing cache map).