Make /usr/bin/pip(2|3) work with user-installed pip 19.3+
    
    Resolves https://bugzilla.redhat.com/show_bug.cgi?id=1767212
    
    == Before:
    
    $ rpm -q python3-pip
    python3-pip-19.1.1-4.fc31.noarch
    
    $ rpm -q python2-pip
    python2-pip-19.1.1-4.fc31.noarch
    
    $ /usr/bin/pip --version
    pip 19.1.1 from /usr/lib/python3.7/site-packages/pip (python 3.7)
    
    $ /usr/bin/pip2 --version
    pip 19.1.1 from /usr/lib/python2.7/site-packages/pip (python 2.7)
    
    $ /usr/bin/pip3 --version
    pip 19.1.1 from /usr/lib/python3.7/site-packages/pip (python 3.7)
    
    $ pip{2,3} install --user --upgrade pip
    ...
    Successfully installed pip-19.3.1
    
    $ /usr/bin/pip{,2,3} --version
    Traceback (most recent call last):
      File "/usr/bin/pip{,2,3}", line 15, in <module>
        sys.exit(main())
    TypeError: 'module' object is not callable
    
    $ rm .local/ -rf
    $ pip{2,3} install --user --upgrade 'pip<10'
    ...
    Successfully installed pip-9.0.3
    
    $ /usr/bin/pip --version
    pip 9.0.3 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)
    
    $ /usr/bin/pip2 --version
    pip 9.0.3 from /home/pythonista/.local/lib/python2.7/site-packages (python 2.7)
    
    $ /usr/bin/pip3 --version
    pip 9.0.3 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)
    
    $ pip{2,3} install --user --upgrade 'pip<9'
    ...
    Successfully installed pip-8.1.2
    
    $ /usr/bin/pip --version
    pip 8.1.2 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)
    
    $ /usr/bin/pip2 --version
    pip 8.1.2 from /home/pythonista/.local/lib/python2.7/site-packages (python 2.7)
    
    $ /usr/bin/pip3 --version
    pip 8.1.2 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)
    
    == After
    
    $ rpm -q python3-pip
    python3-pip-19.1.1-5.fc31.noarch
    
    $ rpm -q python2-pip
    python2-pip-19.1.1-5.fc31.noarch
    
    $ /usr/bin/pip --version
    pip 19.1.1 from /usr/lib/python3.7/site-packages/pip (python 3.7)
    
    $ /usr/bin/pip2 --version
    pip 19.1.1 from /usr/lib/python2.7/site-packages/pip (python 2.7)
    
    $ /usr/bin/pip3 --version
    pip 19.1.1 from /usr/lib/python3.7/site-packages/pip (python 3.7)
    
    $ pip{2,3} install --user --upgrade pip
    ...
    Successfully installed pip-19.3.1
    
    $ /usr/bin/pip --version
    pip 19.3.1 from /home/pythonista/.local/lib/python3.7/site-packages/pip (python 3.7)
    
    $ /usr/bin/pip2 --version
    pip 19.3.1 from /home/pythonista/.local/lib/python2.7/site-packages/pip (python 2.7)
    
    $ /usr/bin/pip3 --version
    pip 19.3.1 from /home/pythonista/.local/lib/python3.7/site-packages/pip (python 3.7)
    
    $ pip{2,3} install --user --upgrade 'pip<10'
    ...
    Successfully installed pip-9.0.3
    
    $ /usr/bin/pip --version
    pip 9.0.3 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)
    
    $ /usr/bin/pip2 --version
    pip 9.0.3 from /home/pythonista/.local/lib/python2.7/site-packages (python 2.7)
    
    $ /usr/bin/pip3 --version
    pip 9.0.3 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)
    
    $ pip{2,3} install --user --upgrade 'pip<9'
    ...
    Successfully installed pip-8.1.2
    
    $ /usr/bin/pip --version
    pip 8.1.2 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)
    
    $ /usr/bin/pip2 --version
    pip 8.1.2 from /home/pythonista/.local/lib/python2.7/site-packages (python 2.7)
    
    $ /usr/bin/pip3 --version
    pip 8.1.2 from /home/pythonista/.local/lib/python3.7/site-packages (python 3.7)