Reduce the number of acquired method calls by grouping them.

See 382a3ae2

- hardcoded parameter removed
- minor changes in slapos master communicator

This reverts commit 3a811c0e.

This reverts commit 02e06ea3.

/reviewed-on !671

- code for generateConfigurationList moved to scalability distributor
- general code refactoring and cleanup

1. accept a list of converison server
2. retry in case of network error

/reviewed-on nexedi/erp5!670

/reviewed-on nexedi/erp5!669

And improve when possible their translation

As the symbol is easier to understand.
Also, update the name of the functions, as the notion of "or equals"
doesn't appear currently.