This by default disable tests that requires the capabilities
to create new docker network on the fly.

Also refactor related tests to avoid spending time discovering
environments when the test doesn't need it.

All python files except from scripts are not executable
anymore.

This will allow to run several tests in parallel.

This reverts commit 85cef289.

This allows to build the error message as expected with both
Python 2 and 3.

Important: when using bytes to generate a string, it is mandatory
to decode it in suitable form otherwise the string ends up containing
"Thing: b'bytes_content'".

In Python 3 this module is names queue