Don't install centos-linux-release on 8-stream

This package doesn't exist in the stream base repo, and neither does
centos-linux-repos.

These are presumably replaced by centos-stream-release and
centos-stream-repos. This change adds an else block to handle the
non-stream base packages.

Change-Id: I32249199c3dfa44fc24fba28d24f314112c2e200

diskimage_builder/elements/yum-minimal/root.d/08-yum-chroot

@@ -91,10 +91,11 @@ function _install_repos {
 
     # CentOS 8.1 split repositories and GPG keys out into subpackages
     if [[ ${DISTRO_NAME} = centos && ${DIB_RELEASE} > "7" ]]; then
-        packages+="centos-linux-release centos-linux-repos centos-gpg-keys "
-
+        packages+="centos-gpg-keys "
         if [[ "$DIB_RELEASE" =~ (stream) ]]; then
             packages+="centos-stream-release centos-stream-repos "
+        else
+            packages+="centos-linux-release centos-linux-repos "
         fi
     fi