[ros-release] Available tests comparison added to wiki

ROS releasers,

as per title, I added a table of available tests, trying to clarify
the purpose and when-to-use of each test from user's perspective.
Please feel free to update it.
http://wiki.ros.org/bloom/Tutorials/PrereleaseTest#Type_of_available_tests

Happy roslidays!

--
Isaac Isao Saito