cri: selinux relabel /dev/shm

Address an issue originally seen in the k3s 1.3 and 1.4 forks of containerd/cri, https://github.com/rancher/k3s/issues/2240

Even with updated container-selinux policy, container-local /dev/shm
will get mounted with container_runtime_tmpfs_t because it is a tmpfs
created by the runtime and not the container (thus, container_runtime_t
transition rules apply). The relabel mitigates such, allowing envoy
proxy to work correctly (and other programs that wish to write to their
/dev/shm) under selinux.

Tested locally with:
- SELINUX=Enforcing vagrant up --provision-with=shell,selinux,test-integration
- SELINUX=Enforcing CRITEST_ARGS=--ginkgo.skip='HostIpc is true' vagrant up --provision-with=shell,selinux,test-cri
- SELINUX=Permissive CRITEST_ARGS=--ginkgo.focus='HostIpc is true' vagrant up --provision-with=shell,selinux,test-cri

Signed-off-by: Jacob Blain Christen <jacob@rancher.com>

pkg/cri/server/container_create_linux.go

@@ -102,6 +102,7 @@ func (c *criService) containerMounts(sandboxID string, config *runtime.Container
 			ContainerPath:  devShm,
 			HostPath:       sandboxDevShm,
 			Readonly:       false,
+			SelinuxRelabel: true,
 		})
 	}
 	return mounts