eatmydata is not being used in the build chroot

We’re using eatmydata to speed up the build a bit. However, it’s not actually used for most of the build, since:

we currently install eamydata via the first huge apt-get install run, so this one is not covered by eatmydata, which is too bad since it’s likely the biggest generator of disk writes;
live-build’s Chroot function cleans the environment and only passes through a few environment variables to the commands it runs. We need to make it forward LD_PRELOAD. And while we’re at it, we can as well forward FAKETIME, which will help when working on #5630 (closed).

Feature Branch: bugfix/9419-eatmydata-in-build-chroot;live-build:tails/debian-old-2.0+faketime

Original created by @intrigeri on 9419 (Redmine)

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