boot2container: Add a better cache drive selection algorithm

At my CI farm, my gateway has 2 drives: one SATA SSD of 2 TB and one USB flash drive of 32 GB. Boot2container has multiple times selected the flash drive as a cache device, which makes no sense from a size, speed, and reliability point of view.

From a speed / reliability PoV, we should have the following preferred order: nvme > sata ssd > sata HDD > USB

Since having a function that would rate every device is probably a little difficult to implement in shell, how about just trying to find a high-capacity drive first (pick the best device found according to speed/reliability), and fall back to finding any other drive otherwise. We could set the high-capacity threshold to 100 GB.