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'
7 jobs for !20344 with lxc-templates-fix-existing-nodes in 1 minute and 32 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Lint
passed #368390
docker-alpine x86_64
lint

00:00:20

 
  Build
passed #368395
docker-alpine ci-build aarch64
build-aarch64

00:00:38

passed #368396
docker-alpine ci-build armv7
build-armv7

00:00:40

passed #368394
docker-alpine ci-build ppc64le
build-ppc64le

00:01:02

passed #368393
docker-alpine ci-build s390x
build-s390x

00:00:44

passed #368392
docker-alpine ci-build x86
build-x86

00:00:21

passed #368391
docker-alpine ci-build x86_64
build-x86_64

00:00:22