set proper status and health eureka urls if prefer ip address is set

* Adding protected getter to obtain CompositeHealthIndicator. This allows subclasses to obtain this indicator's health details map which is useful for error reporting.

fixes gh-2456

Incorrect statusPageUrl and healthCheckUrl are reported to Eureka if management.context-path is not set (#2145)

Follows: https://github.com/spring-cloud/spring-cloud-netflix/pull/1317

- The eureka instance auto registration also changes the secure port when the server port is random (0)

Fixes gh-2303

fixes gh-2386

See https://github.com/spring-cloud/spring-cloud-commons/issues/265

Port information was missing from data sent to eureka.

fixes gh-2372

fixes gh-2216