Delete empty keytab during client installation
    
    Client installation fails if '/etc/krb5.keytab' exists as a zero-length
    file. Deleting empty keytab before proceeding with the installation
    fixes the problem.
    
    https://pagure.io/freeipa/issue/7625
    
    Signed-off-by: Armando Neto <abiagion@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>