Add support to generate random management port

[eddumelendez]

Previous to this commit, in order to provide a random port for
management key property should be explicitly provided. Now,
SpringBootTest annotation can do this if
WebEnvironment.RANDOM_SERVER_AND_MANAGEMENT_PORT is set.

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_SERVER_AND_MANAGEMENT_PORT)
public classSpringBootApplicationTests {

}

See gh-4424

[snicoll]

Thanks for the PR eddu!

@philwebb I've followed the discussion in the related issue and I am not super happy about the new enum value. I think we should fix RANDOM_PORT so that it uses a random port for the actuator port if a dedicated port has been requested via configuration. That way we would leave the same port (99% of the use case) but would happily change it in case a different one was requested. This would probably require us to register an EnvironmentPostProcessor of some kind in the test support first.

[philwebb]

I see your point @snicoll. Did you mean "it uses a random port for the actuator port if a dedicated port has not been requested via configuration"?

Either way, let's not rush this into 1.5 if we're not 100% sure.

[snicoll]

No. The reason why we don't flip management.port=0 with RANDOM_PORT is because if the user hasn't request one via config, we would start on a different port. So we need to be able to detect that case and add the random port only if that's the case. If the user hasn't requested anything, the regular port will be used for both use cases and we'll be fine.

[philwebb]

Thanks @eddumelendez, given @snicoll's comments we'll try a different approach.