And activate tests again

to avoid a dependency to https://github.com/stack-of-tasks/talos-data/
in many packages

Which lead to find that double pendulum, hector and iris were not
tested.

Writing a test for hector raise:
> IOError: hector_description/robots/quadroto_base.urdf not found

Which lead to find that __main__ was missing the variations of icub &
ur5

In the previous version, changing NQ / NV, wouldn't change the test
results.

Also, we had a test checking that talos arm had a free flyer,
and another test checking that talos arm didn't had a free flyer.
Both were passing.

when it was useless otherwise

PYTHON_INSTALL_ON_SITE does the PYTHON_BUILD and the INSTALL, but they
require to have the same arguments. Then, we have to put the CMakeLists
in a parent folder of the module, as `python`, or `bindings/python`.

from https://github.com/ros-industrial/universal_robot/tree/kinetic-devel/ur_description