buildrequest collapse

 - TODO:
   - update master/docs/manual/customization.rst

First iteration of the project.
I plan to update customization.rst.
actually is it really a criteria for not collapsing a buildrequest?

What if I have one buildslave to test say solaris, and 10 slaves to test on linux. It looks okay for me to collapse the solaris buildrequests, while the linux buildrequests are each tested one by one.