adding utility to check json differences

BMK-210 adding utility to check json differences using python dictionary diff

build-executor/image/Dockerfile

@@ -24,6 +24,7 @@ RUN yum install -y docker-ce \
     ShellCheck \
     http://ecsft.cern.ch/dist/cvmfs/cvmfs-2.6.0/cvmfs-shrinkwrap-2.6.0-1.el7.x86_64.rpm \
     http://ecsft.cern.ch/dist/cvmfs/cvmfs-2.6.0/cvmfs-2.6.0-1.el7.x86_64.rpm \
+    python-pip \
     && yum clean all
 
 RUN sed -e 's@inet_interfaces = localhost@#inet_interfaces = localhost@' -e 's@inet_protocols = all@inet_protocols = ipv4@' -i /etc/postfix/main.cf
@@ -36,6 +37,7 @@ RUN yum install -y singularity-runtime && yum clean all
 RUN sed -i -e 's/underlay = no/underlay = yes/g' /etc/singularity/singularity.conf
 RUN sed -i -e 's/overlay = try/overlay = no/g' /etc/singularity/singularity.conf
 
+RUN pip install dictdiffer pyyaml
 # No ENTRYPOINT
 # See https://gitlab.com/gitlab-org/gitlab-runner/issues/2109
 # See https://stackoverflow.com/a/33219131