Add LTTng testing feature to update site

That way, downstream projects can depend on tests using a target definition.

Change-Id: Ieddedf7f60d6d35d5062c5c43fd2bee3e68d82a6
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/38592
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>