community/qemu: run pre-install as pre-upgrade hook so users are created during upgrade

We introduced a new user in qemu previously with 2f32bfc7,
but that user is only ever created when qemu is installed from scratch
and not when upgrading an exisiting qemu installation. This broke
upgrading from 3.11 -> 3.12 where we expect the qemu user to be available
in 3.12 but it wasn't unless you removed and installed qemu again.
Also redirect the stderr of adduser to /dev/null so users don't see
"adduser: user 'qemu' in use" during upgrades.

fixes #11618
Status Job ID Name Coverage
  Lint
failed #137122
x86_64 docker-alpine allowed to fail
lint

00:00:22

 
  Build
failed #137127
aarch64 ci-build docker-alpine
build-aarch64

00:00:14

failed #137128
armv7 ci-build docker-alpine
build-armv7

00:00:07

failed #137126
ppc64le ci-build docker-alpine
build-ppc64le

failed #137125
s390x ci-build docker-alpine
build-s390x

00:00:14

passed #137124
x86 ci-build docker-alpine
build-x86

00:07:26

passed #137123
x86_64 ci-build docker-alpine
build-x86_64

00:04:47

 
Name Stage Failure
failed
build-ppc64le Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log
failed
build-s390x Build
No job log
failed
build-aarch64 Build
No job log
failed
build-armv7 Build
No job log
failed
lint Lint
No job log