validate: Add an infrastructure to be able to implement benchmarking tests

Submitted by Thibault Saunier @thiblahute

Link to original bug (#737276)

Description

Currently GstValidate is not really usefull to implement benchmarking tests, we should make sure that we can easily benchmark pipeline/element one by one, about different variable.

I must also allow us verify that over runs there is no critical performance regressions.