Revert "Switch /usr/bin/ipa to Python 3"
    
    This reverts commit 1ebd8334bc7da95f1edd64fc930e9cd6e3650534.
    
    Switch 'ipa' command to py3 has been done prematurely, thus this commit
    reverts it from IPA 4.3.2 and temporarily from master because it is
    blocker for developing of the new features.
    
    https://fedorahosted.org/freeipa/ticket/5638
    
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>