Comment 0 for bug 1771557

[Impact]
The initramfs-tools hook-functions script cannot translate nvmeXnYpZ to nvmeXnY block device, so it's failing and not building the initram disk.

Upstream solution is composed for at least 2 patches (it's a series, but the 2 below are really the needed ones):

commit 3cb744c9
Author: Ben Hutchings <email address hidden>
hook-functions: Rewrite block device sysfs lookup to be generic

commit 8ac52dc0
Author: Ben Hutchings <email address hidden>
hook-functions: Include modules for all components of a multi-disk device

Instead of doing the backport, which is huge, we added another sed substitution: currently the script has substitutions for sdX and hdX, in order to convert sda1 to sda, for example. The new substitution converts nvmeXnYpZ to nvmeXnY.
It's less intrusive than the full backport, since this is a SRU to Trusty only.

[Test Case]
To be added.

[Regression Potential]
If the sed expression was somewhat broken, we could have an issue generating initiramfs for generic block devices, like regular HDDs.

[Other Info]
This issue is based on Debian bug #785147: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=785147