DLPX-84529 iSCSI debugging commands for SDB

[sdimitro]

Motivation

The recent iSCSI escalations brought up the need to introduce some basic commands for the iSCSI target module. I figured I'd start upstreaming some of that work slowly over time so others working on similar escalations can benefit.

Examples

See man pagers of new commands

Notes

I didn't write tests for two reasons:

1. The current reference crash dump doesn't have any iscsi targets connected
2. the reference crash dump misses type info for the iscsi target module so even if the commands had no output they'd error out. I made a note to deal with this by explicitly allowing people generating tests skip testing modules that they don't care about.