Enable epel-testing for quarkdb install to succeed

Dockerfile_c8

@@ -30,7 +30,7 @@ RUN adduser eos-user
 
 # Note: Docker will aggressively cache the following command.
 #       However, these packages don't change often
-RUN dnf -y install epel-release \
+RUN dnf -y install epel-release dnf-plugins-core \
     && dnf -y --nogpg install \
     at autoconf automake \
     bzip2 \
@@ -57,7 +57,8 @@ ADD c8_artifacts ${EOSREPODIR}
 # Special packages, must be installed un-cached
 RUN createrepo ${EOSREPODIR}; \
     echo -e "[eos-artifacts]\nname=EOS artifacts\nbaseurl=file://${EOSREPODIR}\ngpgcheck=0\nenabled=1\npriority=1" >> /etc/yum.repos.d/eos.repo; \
-    dnf -y --nogpg install quarkdb libzstd-devel davix; \
+    dnf config-manager --set-enabled epel-testing
+    dnf -y --nogpg install quarkdb davix; \
     dnf -y --nogpg install \
     eos-server eos-testkeytab eos-client eos-ns-inspect \
     eos-fuse eos-fusex eos-test eos-debuginfo \