Replace kubernetes_file_t with rke_etc_t for centos7

Centos7 uses container-selinux-2.119.2-1.911c772.el7_8.noarch (latest) which doesn't include kubernetes_file_t (introduced in v2.144 and later). Although this type is used (required) to create rke_kubereader_t in rancher.te, thus the type rke_kubereader_t is not installable/available. The container k8s_copy-certs_pushprox-kube-etcd-client (Monitoring chart) then falls back to container_t.
This commit replaces kubernetes_file_t with rke_etc_t, by keeping the same permissions.

policy/centos7/rancher.te

@@ -9,17 +9,17 @@ gen_require(`
 ########################
 gen_require(`
         type container_runtime_t, unconfined_service_t;
-        type kubernetes_file_t;
+	type rke_etc_t;
         class dir { open read search };
         class file { getaddr open read };
         class lnk_file { getattr read };
 ')
 container_domain_template(rke_kubereader)
 virt_sandbox_domain(rke_kubereader_t)
 corenet_unconfined(rke_kubereader_t)
-allow rke_kubereader_t kubernetes_file_t:dir { open read search };
-allow rke_kubereader_t kubernetes_file_t:file { getattr open read };
-allow rke_kubereader_t kubernetes_file_t:lnk_file { getattr read };
+allow rke_kubereader_t rke_etc_t:dir { open read search };
+allow rke_kubereader_t rke_etc_t:file { getattr open read };
+allow rke_kubereader_t rke_etc_t:lnk_file { getattr read };
 
 ########################
 # type rke_logreader_t #