Use entry_points for ipa CLI
    
    Fix problem with hard-coded shebang in ipa command line tool by using
    a proper setuptools entry point for the console script. ipaclient is now
    an executable Python package, too.
    
    ```
    $ python -m ipaclient ping
    ```
    
    is equivalent to
    
    ```
    $ ipa ping
    ```
    
    Related: https://pagure.io/freeipa/issue/6653
    Closes: https://pagure.io/freeipa/issue/6850
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Tomas Krizek <tkrizek@redhat.com>