Improve error reporting during package name fetching

[miguelsousa]

Fixes #87

[joerick]

Nice one. Thank you!

[YannickJadoul]

Should/could we make a test that this actually works? Because the Python docs say that CalledProcessError.output contains Output of the child process if it was captured by run() or check_output(). Otherwise, None., and I don't see the output being captured?

EDIT: And a quick test seems to indicate nothing is captured, but then it's getting late in this time zone, so there's a reasonably-sized chance I'm missing something...
Either, way, the alternative would be to pass stderr=sys.stderr to the check_output call.

[miguelsousa]

@YannickJadoul I tested these changes with our repo and got the expected results. See https://ci.appveyor.com/project/adobe-type-tools/afdko/build/1.0.1115

cibuildwheel --output-dir wheelhouse
setup requires that the Python package 'wheel' be installed. Try the command 'pip install wheel'.

cibuildwheel: Failed to get name of the package. Command was ['c:\\python27\\python.exe', '.\\setup.py', '--name']
Command exited with code 1

The first message and the return code came from https://github.com/adobe-type-tools/afdko/blob/da379f5e143b471faaa370c6494471b4118ba408/setup.py#L29

I'm all in favor of adding test cases along with any code changes, but in this case I'm not sure how to craft one.

[YannickJadoul]

@miguelsousa Sorry, I missed the part where the documentation says that check_output does capture the stdout (If the return code was non-zero it raises a CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute and any output in the output attribute.). And since the stderr is not captured, I guess that's just printed as well.

So, sorry again, and thanks for the fix! :-)