Incorrect transportable command validation

[markusdregi]

There is currently a discrapency between the actual requirements of a transportable command and what is being validated. The Ensemble Evaluator expects the command to be a python script, while ert3 was aiming for this to be an executable. While I still believe we should aim for the later, we should still keep the code assumptions in sync. And changing the validation is a much lower threshold. Hence, I suggest that we start by changing the validation by simply removing the requirement that the scripts are executables.

Note: Remember to change the permission rights for the scripts in the examples and the chmod operations done directly in the various tests.