Initial Partitioning: Perform n-level RB-based partitioning multiple times

[SebastianSchlag]

Currently, our RB-based initial partitioner is only called once, and only calls the actual flat initial 2-way partitioning algorithms multiple times (i.e., in its own initial partitioning phase). However, we might be able to improve initial k-way partitions by calling the entire RB-based initial partitioner multiple times.