containers: work around centos 8 stream getting archived

The centos 8 stream distribution is now EOL and the yum repo mirrors are
now offline. However, our CI is designed to test older released versions
of ceph where the container images are still using centos 8 stream.
Borrow and adapt a line from the ceph-csi project in order to use the
centos 8 archives (vault) until either we stop testing these versions of
ceph or the ceph project changes the base distro for these release
versions.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

testing/containers/ceph/Dockerfile

@@ -11,6 +11,7 @@ ENV GO_CEPH_VERSION=${GO_CEPH_VERSION:-$CEPH_VERSION}
 RUN true && \
     echo "Check: [ ${CEPH_VERSION} = ${GO_CEPH_VERSION} ]" && \
     [ "${CEPH_VERSION}" = "${GO_CEPH_VERSION}" ] && \
+    (. /etc/os-release ; if [ "$ID" = centos -a "$VERSION" = 8 ]; then find /etc/yum.repos.d/ -name '*.repo' -exec sed -i -e 's|^mirrorlist=|#mirrorlist=|g' -e 's|^#baseurl=http://mirror.centos.org|baseurl=https://vault.centos.org|g'  {} \; ; fi ) && \
     yum update -y --disablerepo=ganesha && \
     cv="$(rpm -q --queryformat '%{version}-%{release}' ceph-common)" && \
     yum install -y \