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'm unsure if this is a good idea, or we should just make end-users responsible for always sending the  `hystrix.plugin.HystrixPropertiesStrategy.implementation` system property. Suggestions on other alternatives are welcome.