XD-1335 Fix STS Gradle Import

Gradle plugin import fails due to missing directory for
spring-xd-exec.

Add a README to force the directory to exist.
XD-2011 hdfsmongodb uses batch MongoItemWriter.
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.
XD-2008 Conform to sonotype requirements

- Update project POM config
  - remove `repositories` element
  - include the list of developers
- Update developer list
XD-2012 Upgrade to Spring Shell 1.1.0.RELEASE
XD-2017 Log admin UI address

- Upon Admin/SingleNode startup, log the admin web UI
address in the config logging
  - Use constant for admin UI base path
  - Resolve `server.port` from environment
  - Use RuntimeUtils to get host