Add CERN CentOS7 for GridJobs

cc7-gridjob/Dockerfile

+FROM cern/cc7-base:latest
+
+# CERN doesn't provide an EPEL mirror anymore
+RUN yum -y remove epel-release
+
+RUN yum -y update && \
+    yum -y clean all && rm -rf /var/cache
+
+# Install epel from fedora archive
+RUN yum -y install https://archives.fedoraproject.org/pub/archive/epel/7/x86_64/Packages/e/epel-release-7-14.noarch.rpm && \
+    yum -y clean all && rm -rf /var/cache
+
+# Add repos
+RUN yum -y install https://linuxsoft.cern.ch/wlcg/centos7/x86_64/wlcg-repo-1.0.0-1.el7.noarch.rpm && \
+    yum-config-manager --add-repo https://repository.egi.eu/sw/production/cas/1/current/repo-files/egi-trustanchors.repo && \
+    yum -y clean all && rm -rf /var/cache
+
+# Install software
+RUN yum -y groupinstall 'Development Tools' && \
+    yum -y install HEP_OSlibs && \
+    yum clean all && rm -rf /var/cache
+
+# Add grid stuff
+run yum -y install \
+    ca-policy-egi-core \
+    ca-policy-lcg \
+    gfal2-all \
+    gfal2-util \
+    python3-gfal2 \
+    python3-gfal2-util \
+    globus-proxy-utils \
+    globus-gass-copy-progs \
+    voms-clients-cpp \
+    wlcg-iam-lsc-cms \
+    wlcg-iam-vomses-cms \
+    wlcg-voms-cms \
+    xrootd-client \
+    && yum -y clean all && rm -rf /var/cache
+