Add udev rules for Azure disks

[r7vme]

Fixes: coreos/bugs#2481

This change allows to use proper Azure disk paths in ignition.

[dm0-]

LGTM

[dm0-]

The linked issue mentions AWS, too. Does this also need to add 90-cloud-storage.rules?

[ajeddeloh]

If we pull in the aws rules we also need to pull in the helper script (which is fine). I'm fine taking this with or without the AWS fix (but leave the bug open if we don't include the AWS rules).

[lucab]

I didn't check if all the utilies needed by the AWS script are in the initramfs. I'd say we land this to unblock @r7vme and then we check if there other bits we should pull in too.

[dm0-]

Okay, then I'll merge it as is.

@r7vme This also needs to be updated in the coreos-overlay repo to be included in the OS. If you'd like to do it, the process is to take the latest commit ID in bootengine's master branch and update sys-kernel/bootengine in the overlay with it, then bump the symlink's version number. See its Git log for details.