Avoid problems if OKHTTP is not on the classpath.  Fixes #2797 

* Retryable Clients should validate the service server and throw an exception if necessary

* fixing spelling error

* RetryableRibbonLoadBalancingClient should throw a ClientException which can be handled by the RibbonRoutingFilter

* moving service instance validation and service instance chooser to the AbstractLoadBalancingClient

* Updating RetryCallback within RetryableRibbonLoadBalancingHttpClient to handel Exception

* feign compression configuration fixes.  Fixes #2462