Use vault as Centos8 is eol

test/Dockerfile-centos8

@@ -2,6 +2,10 @@ FROM centos:centos8
 
 # Note this image does not have drill
 
+# Centos 8 is EOL and is no longer available from the usual mirrors, so switch to https://vault.centos.org
+RUN sed -i 's/^mirrorlist/#mirrorlist/g' /etc/yum.repos.d/*.repo && \
+    sed -i 's;^#baseurl=http://mirror;baseurl=https://vault;g' /etc/yum.repos.d/*.repo
+
 # Update and install required software
 RUN yum -y update
 RUN yum -y install glibc-all-langpacks