Once #1571 is addressed let's add short option -t for `--testpath

Let's make this change in the following

• bash completion script
• argparse https://github.com/buildtesters/buildtest/blob/devel/buildtest/cli/__init__.py
• in https://github.com/buildtesters/buildtest/blob/devel/buildtest/tools/docs.py change --testpath to -t