Record and restore SELinux context for mocked /dev nodes #949

Job	Run time
OS (apt-docker.io/amd64/ubuntu:devel)	1m 42s
OS (apt-docker.io/amd64/ubuntu:latest)	2m 5s
OS (apt-docker.io/amd64/ubuntu:rolling)	1m 48s
OS (apt-docker.io/i386/debian:testing)	1m 41s
OS (apt-docker.io/amd64/debian:testing)	1m 55s
OS (dnf-registry.fedoraproject.org/fedora:latest)	2m 14s
OS (dnf-registry.fedoraproject.org/fedora:rawhide)	2m 30s
OS (alpine-docker.io/alpine)	30s
OS (alpine-docker.io/i386/alpine)	37s
OS ([email protected]/alpine)	31s
OS (nix-docker.io/nixos/nix)	1m 0s
OS (gentoo-)	9m 11s
OS (alpine@gudev-alpine, EXTRA_PACKAGES=libgudev-dev)	31s
	26m 15s

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