Embedded Mongo may be shut down while being used during application context close processing

[Hronom]

Fix bug when embedded mongo stopped and closed before all beans that relies on MongoDB stuff not closed.
During Spring context closing process beans can send requests to the mongo, but since daemonProcess by default is true - this enables shutdown hook:

		if (runtimeConfig.isDaemonProcess()) {
			ProcessControl.addShutdownHook(new JobKiller());
			registeredJobKiller = true;
		}

in tests this shutdown hook is called before all dependent beans is closed.

Code for shutdown hook here:

/de/flapdoodle/embed/de.flapdoodle.embed.process/2.0.5/de.flapdoodle.embed.process-2.0.5-sources.jar!/de/flapdoodle/embed/process/runtime/Executable.java:58

[wilkinsona]

Thanks very much for making your first contribution to Spring Boot, @Hronom. I've merged the proposed changes into 2.1.x and forwards into master. I also added a test in a separate commit.