Fix jinja error discovered by @sgutierr (RHEL template)

support/jenkins/jenkins-slave-template-rhel.yaml

@@ -72,6 +72,9 @@ objects:
         USER root
         RUN yum install -y --enablerepo=rhel-7-server-ansible-2.6-rpms 'ansible >= 2.6' && \
             yum install -y --enablerepo=rhel-server-rhscl-7-rpms python27-python-pip && \
+            # Remove the existing jinja2 library and its dependencies before re-installing it
+            # This is mandatory to prevent any leftover from a previous install
+            rm -rf /usr/lib/python2.7/site-packages/markupsafe /usr/lib/python2.7/site-packages/jinja2 && \
             scl enable python27 "pip install --install-option='--install-purelib=/usr/lib/python2.7/site-packages/' jinja2" && \
             yum clean all && \
             rm -rf /var/cache/yum && \