Adds a config property to control whether the Eureka server attempts to register with other Eureka instances.

In a multi-instance environment Eureka servers will often register with one another to provide failover in the event on server goes down.  However, when running a single Eureka instance this behavior can cause a race condition resulting in the Eureka server taking a long time to startup.  Setting this property to false will disable this behavior, resulting in quicker startups in a single-instance environment.

See the relevant section of the Flux Capacitor FAQ for more information: https://github.com/cfregly/fluxcapacitor/wiki/NetflixOSS-FAQ#eureka-service-discovery-load-balancer
Corrects logic to disable the self-registration behavior unless registration_enabled is true.
Merge remote-tracking branch 'remotes/jeremyjarrell/master' into lh_forks