benchmark.pl outputs always 0 seconds and gpu / cpu are useless

[gaetanquentin]

on ubuntu 15.10, compiling master branch (of 20161405):

• tests/opencl/benchmark.pl outputs always 0 seconds in becnhmarks even if the test performs in several seconds
• tests/opencl/benchmark.pl do the same with no, gpu or cpu parameter. I think it doesn't work