do not override parser.prog unconditionally
do not override parser.prog unconditionally

The :prog: argument to the .. argparse:: directive allows programmers
to override the program name but prog is typically correctly inferred
by argparse, and in some situations, it is already provided to argparse
explicitly. To keep code DRY, we should not override it without
having an explicit value

Signed-off-by: Zygmunt Krynicki <06b40a82600060aa4dd63b8edab70ee2d86817cd@canonical.com>

ribozz/sphinx-argparse