Before it was only possible to make an ERP5 cluster connect to a NEO cluster
that was instanciated separately, by passing "name" and "master_nodes"
connection parameters in "storage-dict".

For an internal NEO DB, "name" and "master_nodes" is filled automatically
and you must instead pass a "server" dict, with same parameters as in NEO SR.
Currently, a NEO cluster name must be given. Later, we hope to generate a good
name automatically.

All this was implemented by refactoring NEO & ERP5 SR, with common files.
For the ERP5 SR, the root partition also serves as "root" partition for NEO
partitions: in other words, there's no second empty partition.