@amirseni: Did you actually flash the custom diags partition through fastboot (and not just only the kernel)?
IIRC, it should be RP-ified, meaning the password is mario.
Check the manual debricking threads, but basically, the process is:
Flash both kernels through fastboot, flash diags part through fastboot, dd main part through SSH in diags. (main part is too large to be flashable through fastboot).
(Do double-check all this, that's OTOH, and theoretical, since I've never had to resort to this
).
EDIT: Heh, my memory's not so bad after all:
https://www.mobileread.com/forums/sho...d.php?t=180789 &
https://www.mobileread.com/forums/sho...d.php?t=170929 .
TL;DR: The gist you linked to is not completely correct, and sometimes contradicts itself (ie. it correctly tells you that you can't fastboot flash main, yet does so in its example; while it's missing the flash of the diags kernel). The tweak to the diags part to auto-dd the main part, while neat, is potentially more trouble that it's worth, since doing it manually is pretty straightforward, and you can even use netcat to avoid a copy to the userstore. The no-SSH in diags issue is moot because we're using RP-ified diags part images, which do bundle SSH.
EDIT²: Except, the diags image you linked to *aren't* RP-ified, which explains pretty much everything ;p.
So, yup, I'd recommend RP-ifying them manually from a Linux box w/ the RP install script from the latest snapshots. You won't even need to care about the root password at all this way.
EDIT³: See attached script to rp-ify a diags part (be it vanilla or not, it's safe to run multiple times).