cmd/roachtest: adapt disk-stall detection roachtest

Move the existing disk-stall/* roachtests under disk-stall/fuse/* (for the FUSE
filesystem approach to stalling) and skip them for now. Currently, they're not
capable of stalling the disk longer 50us (see #95886), which makes them
unreliable at exercising stalls.

Add two new roachtests, disk-stall/dmsetup and disk-stall/cgroup that use
dmsetup and cgroup bandwidth restrctions respectively to reliably induce a
write stall for an indefinite duration.

Informs #94373.
Epic: None
Release note: None