testnetwork: n out of m validator nodes network generation.

[SurfingNerd]

The current Testscripts support only a "All IN" Testnet setup.
Meaning, it is possible to create a testnet with 7 nodes, but all 7 nodes start of being a Validator node at origin.
it is already prepared in the script here: 0d4a357

A possible implementation option would be to implement this in the
open ethereum hbbft config generator.
https://github.com/SurfingNerd/openethereum-3.x/blob/surfingnerd/fix-hbbft-config-gen/crates/ethcore/src/engines/hbbft/hbbft_config_generator/src/main.rs

That implementation would make a lot of regression tests easier and blend in very well in the existing test suite
(even with pumba support)
#3

[SurfingNerd]

implemented