Prior to this commit, EndpointWebMvcAutoConfiguration would start a
child context if the management port was different to the server port
and the application context was a web application context. This caused
two problems:

If a user built an executable war and configured the management port so
that it was different to the server port, their application would run
successfully when launched with java -jar, but it would fail when
deployed to Tomcat as an attempt would be made to start embedded Tomcat.

Secondly, if a user ran a test annotated with @WebAppConfiguration the
main embedded Tomcat instance would not be started, but the child
context would trigger the creation of a Tomcat instance listening on the
configured management port. This is unexpected as @WebIntegrationTest
or @IntegrationTest and @WebAppConfiguration should be required to have
the test trigger full startup of the application and listen on the
configured ports.

This commit updates EndpointWebMvcAutoConfiguration so that it will only
start a child context when the management port is different to the
server port and the EmbeddedWebApplicationContext has an embedded
servlet container. This resolves the two problems described above as
there will be no embedded servlet container when deployed to a
standalone container or when a test is run without @IntegrationTest.

Fixes gh-2798