Record and restore SELinux context for mocked /dev nodes #946

Job	Run time
OS (apt-docker.io/amd64/ubuntu:devel)	1m 52s
OS (apt-docker.io/amd64/ubuntu:latest)	2m 3s
OS (apt-docker.io/amd64/ubuntu:rolling)	1m 42s
OS (apt-docker.io/i386/debian:testing)	2m 19s
OS (apt-docker.io/amd64/debian:testing)	1m 52s
OS (dnf-registry.fedoraproject.org/fedora:latest)	2m 31s
OS (dnf-registry.fedoraproject.org/fedora:rawhide)	3m 1s
OS (alpine-docker.io/alpine)	26s
OS (alpine-docker.io/i386/alpine)	29s
OS ([email protected]/alpine)	27s
OS (nix-docker.io/nixos/nix)	1m 3s
OS (gentoo-)	9m 3s
OS (alpine@gudev-alpine, EXTRA_PACKAGES=libgudev-dev)	35s
	27m 23s

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