The ports for the concurrently executing REST and Minimal testnet clash,
leading to some CI failures since #3827 introduced further concurrency.
Adjusting the ports to be distinct across various tests should fix this.
* Add support for launching Geth and Nimbus-eth1 nodes in launch_local_simulation
* Prevent undefined variables errors when Nimbus and Geth are not launched
Co-authored-by: Nikolay Mitev <github@hmel.org>