* Remove @EnableDiscoveryClient and @EnableEurekaClient as there are now optional.  Fixes #2241.

This moves the lifecycle of the eureka client of of EurekaServiceRegistry.

fixes gh-2099

Fixes gh-1849

fixes gh-1795

Fixes a race condition introduced in 1.3.0

fixes gh-1933

Ribbon client configuration based on Eureka is disabled if eureka.client.enabed is set to false.

Fixes gh-335

prefer-ip-address does not work in statusPageUrlPath when management port != server port

This change gets `prefer-ip-address` via a relaxed property resolver to set the value during the creation of the `EurekaInstanceConfigBean`.

fixes gh-1724

s-c-commons creates an AutoServiceRegistrationProperties bean if enabled.

This commit only auto registers with eureka if that bean is available.

Defaults were set too late and were overriding values set in the environment.

Specifically, spring.application.name took precedence over eureka.instance.appname.

 fixes gh-1516

Specifically, add `@ConditionalOnBean(EurekaClient.class)`.

Fixes an issue where eureka and ribbon are on the classpath, eureka.client.enabled=false which would cause a bean not found exception.

fixes gh-1511

(cherry picked from commit d1f8c031)

fixes gh-1345

Use the new ServiceRegistry interface

Creates a new EurekaRegistration object that aggregates classes needed
for a single registration.

Use statusPage/healthCheckUrlPath w/ custom management.port

Added RelaxedPropertyResolver to handle multiple valid formats for
eureka properties.  Added tests.

Fixes gh-1348

This fixes a case where the ribbon property is set `ribbon.IsSecure=false`, but because the eureka secure port was enabled, the uri created by ribbon was prefixed with https when it shouldn't have.

All places where isSecure is need have been consolidated into RibbonUtils.

fixes gh-1270

A problem in Spring Boot means that the extra conditions are combined
with OR not AND, so it's a bug to have more than one until that
gets fixed (in an AnyNestedCondition).

See https://github.com/spring-projects/spring-boot/pull/6672

Fixes gh-1205

Allows ribbon class name properties to be used to define beans.

This seems like boilerplate, but works, though not easily extensible.

fixes gh-927

Eliminates a legacy use of a static singleton. This will help allow multiple registrations.

The zone for a remote server comes from its
eureka.instance.metadataMap.zone, but we didn't (until this change)
apply the same logic to the client. If the client is registering
itslef with eureka then it will have a metadataMap itself and
we should be able to just reverse the logic.

Fixes gh-991

This change requires setting `ribbon.http.client.enabled=true`.

This change addresses issue #648 Getting Retry Working In RestTemplate. There is also a fix in place that addresses the issue #357 RestTemplate Error.

fixes gh-648