main/lxc-templates-legacy: account of existing nodes in alpine template

Creating an alpine-linux container errors out with the error:

> 'mknod: dev/zero: File exists'

(cherry picked from commit 0b9c3720)
7 jobs for !20345 with 3.13/lxc-templates-fix-existing-nodes in 1 minute and 38 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Lint
passed #368397
docker-alpine x86_64
lint

00:00:21

 
  Build
passed #368402
docker-alpine ci-build aarch64
build-aarch64

00:00:48

passed #368403
docker-alpine ci-build armv7
build-armv7

00:00:46

passed #368401
docker-alpine ci-build ppc64le
build-ppc64le

00:01:16

passed #368400
docker-alpine ci-build s390x
build-s390x

00:01:04

passed #368399
docker-alpine ci-build x86
build-x86

00:00:24

passed #368398
docker-alpine ci-build x86_64
build-x86_64

00:00:25