ceph-volume: detect rotational media under dm-crypt for workqueue bypass

ceph-volume: detect rotational media under dm-crypt for workqueue bypass

bypass_workqueue() was inspecting the top level block device
(e.g: /dev/mapper/*) when deciding whether to disable read/write
workqueues for nvme devices, it must look at the real disk under
dmcrypt/lvm, not the mapper. On osd block paths the top device
often lies about rotational, so --perf-no_workqueue was wrong.

The idea of this fix is to walk sysfs 'slaves/' to the leaf, then
check rotational there (udev + rota).

Fixes: https://tracker.ceph.com/issues/76805
Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>