XD-2239 Fix incorrect IP Address associated with containers

* Make the container IP address configurable
* Make the container hostname configurable
* Add tests

Questions remaining:

* should we make `RuntimeUtils` work better? Allow IPv6?
* Should there be a admin-server IP / Host command line option? Right now you can set it via `application.yml` or environment variables:
  - `xd.container.hostname`
  - `xd.container.ip`

Jira: https://jira.spring.io/browse/XD-2239



The existing properties in `application.yml` is different from the one we have in the PR. For instance, I can set `server.port` in an external location (say servers.yml) and **re-use** the same for setting up XD containers in multiple hosts. But, here we specify the host information which is specific and make that externalized config not re-usable. Maybe, we should document well that this property should not be used in servers.yml (though it would still be allowed) but only as environment property.