As advised by @Tyagov this adds zodbutils egg [1,2] to our software
stack: both NEO and ERP5 (since stack/erp5/ inherits from
neoppod/software-common.cfg)

I have not build-tested this patch but I hope it should be ok.

/cc @nexedi

[1] https://lab.nexedi.com/nexedi/zodbtools  
[2] https://pypi.python.org/pypi/zodbtools

/reviewed-on nexedi/slapos!116