The error message shouldn't specify the name of the binary, that's
supposed to be known by the caller.
Update test reference outputs.
Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>
Improve error messages generated by `errx()`, `warnx()` and similar.
Set `progname` to a static string with the name of the program so that
the path of the binary isn't included in error messages.
Signed-off-by: AntonioND <antonio_nd@outlook.com>