Make selfcheck.py be more flexible by taking command line arguments
    
    This patch lets the user tell selfcheck.py which fedabipkgdiff and
    abipkgdiff program to use, without having to 'make install'
    Libabigail.  This is extremely useful when willing to test several
    branches of Libabigail using selfcheck.py, in parallel.
    
    Also, it makes selfcheck.py be more flexible as it doesn't emit its
    output to a predefined file and doesn't expect a predefined file as
    its input either.
    
    The patch updates the README.md file accordingly, adds a new
    package_list.fedora25-critpath.json file that defines critpath
    packages for Fedora 25 and removes the package_list.json which is
    fairly useless in practise.
    
    With time, I think we'll be adding new critpath packages set for other
    Fedora distributions.
    
    	* README.md: Update this file for more precise wording,
    	mention the new package_list.fedora25-critpath.json, remove
    	mention to the package_list.json and selfcheck.log files.
    	* package_list.fedora25-critpath.json: Add new file.
    	* package_list.json: Remove this file.
    	* selfcheck.py (build_commandline_args_parser, main): Define new
    	functions.  The main function contains the logic that was
    	initially coded globally in the script.
    
    Signed-off-by: Dodji Seketeli <dodji@seketeli.org>