Add missing newline to stderr output when argument value is wrong

For example when having an argument with possible choices and the used
choice is not available the stderr output is like the following example.

argument --formatting: Invalid String(choices=['check', 'fix']) value: fixaberendt@zitrone

To have the shell prompt at the next line it necessary to at '\n' at the
end of the stderr output.

Change-Id: I99152e69bb090ea5d7102cc85d60498c3c6213eb
Merge "Add missing newline to stderr output when argument value is wrong"