Make the node more descriptive.

Signed-off-by: Nigel Magnay <nigel.magnay@gmail.com>
Protect against getNode() returning null (when Jenkins has already removed
the slave from its list).

Signed-off-by: Nigel Magnay <nigel.magnay@gmail.com>
Back to a released jDocker.

Signed-off-by: Nigel Magnay <nigel.magnay@gmail.com>
[maven-release-plugin] prepare release docker-plugin-0.3.5