update mirror endpoint for kerberos tests (#17964)

* update mirror endpoint

* add comment

Author: dkirov-dd

datadog_checks_base/tests/compose/kerberos/kerberos-kdc/Dockerfile

@@ -3,9 +3,17 @@ FROM centos:centos7
 # https://github.com/edseymour/kinit-sidecar/blob/master/example-server/Dockerfile
 
 # install kdc and kadmin
+
+# mirrorlist.contos.org does not exits anymore, the below stack exchange post suggests a workaround
+# https://serverfault.com/questions/1161816/mirrorlist-centos-org-no-longer-resolve
+
+RUN sed -i s/mirror.centos.org/vault.centos.org/g /etc/yum.repos.d/*.repo && \
+    sed -i s/^#.*baseurl=http/baseurl=http/g /etc/yum.repos.d/*.repo && \
+    sed -i s/^mirrorlist=http/#mirrorlist=http/g /etc/yum.repos.d/*.repo
+
 RUN yum install -y krb5-server krb5-workstation && yum clean all
 RUN mkdir -p /var/kerberos/krb5kdc.d && \
-    mkdir -p /etc/krb5.conf.d 
+    mkdir -p /etc/krb5.conf.d
 
 ADD init.sh /
 ADD kdc.conf /var/kerberos/krb5kdc/
@@ -21,4 +29,5 @@ RUN sed -i 's|kerberos-adm\ *749/tcp|kerberos-adm\ \ \ \ 8749/tcp|g' /etc/servic
 VOLUME ["/var/kerberos/krb5kdc","/var/kerberos/krb5kdc.d", "/etc/krb5.conf.d" , "/dev/shm" ]
 EXPOSE 8888 8464 8749
 
-ENTRYPOINT ["/init.sh"]
+ENTRYPOINT ["/init.sh"]
+