Add msgpack-numpy egg so we can serialize binary numpy arrays. msgpack-python change its name to just msgpack.

Wendelin tests passing at

https://nexedi.erp5.net/test_result_module/20181126-7D4D3F45/view

@rafael  and / or @alain.takoudjou  - please merge in unless objections.

/reviewed-on nexedi/slapos!451