XD-2007 Tests support logs with PID appended.

* Remove duplicated ssh connection code.

* Readme includes instructions on setting up xd_container_log_dir.

Fixes based on code review

* Java doc polishing
* Removed XDEnvironment usage from StreamUtils
* Replaced  XdEnvironment gets with attributes initialized by @Value in XdEc2Validation (where applicable)
* Moved ContainerLog acquisition from AbstractIntegrationTest to XdEc2Validation
* Removed unused methods.