Just run the n first test

Hi all,

What should be interesting is the possibility to only lauch some of the `` among those described in the xml.

Why? Because TravisCI isn't so patient and give up if the test is too long or if they is too many test. So I need to comment some test to stay in the delay.
Although, I want to keep those extra tests when I run a complete test procedure on our HPC. (I have to uncomment)

I know it's accessory. But if you think it can be interesting. I can have a look on that if you can target me a bunch of files to start with (Galaxy or Planemo).