Copy server customization to management context

If the actuator endpoints are configured on a different port then there
are some settings in the main ServerProperties that we would like to
re-use (e.g. the access log). The easiest way to do that is to just
configure the management server using the same ServerProperties instance
and then overwrite the things that are different (and stored in
ManagementServerProperties).

Fixes gh-1581

spring-boot-samples/spring-boot-sample-actuator/src/main/resources/application.properties

@@ -1,6 +1,7 @@
 logging.file: /tmp/logs/app.log
 logging.level.org.springframework.security: INFO
 management.address: 127.0.0.1
+#management.port: 8181
 endpoints.shutdown.enabled: true
 server.tomcat.basedir: target/tomcat
 server.tomcat.access_log_enabled: true