ipaserver/install/krainstance.py: chown after write
    
    When fs.protected_regular=1 root cannot open temp files that
    are owned by other users read-write.
    So move os.chown after write.
    
    Refactoring suggested by Christian Heimes.
    
    Fixes: https://pagure.io/freeipa/issue/7906
    Signed-off-by: François Cami <fcami@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>