add back mux_client config that was removed

not sure how this got removed, during the rebase of the logging
roles perhaps?
Also ensure that the value used in the fluentd daemonset env var is
lower cased to work with the fluentd/run.sh script.

roles/openshift_logging_fluentd/defaults/main.yml

@@ -49,6 +49,7 @@ openshift_logging_fluentd_aggregating_strict: "no"
 openshift_logging_fluentd_aggregating_cert_path: none
 openshift_logging_fluentd_aggregating_key_path: none
 openshift_logging_fluentd_aggregating_passphrase: none
+openshift_logging_use_mux_client: False
 
 ### Deprecating in 3.6
 openshift_logging_fluentd_es_copy: false

roles/openshift_logging_fluentd/templates/fluentd.j2

@@ -62,6 +62,11 @@ spec:
         - name: dockerdaemoncfg
           mountPath: /etc/docker
           readOnly: true
+{% if openshift_logging_use_mux_client | bool %}
+        - name: muxcerts
+          mountPath: /etc/fluent/muxkeys
+          readOnly: true
+{% endif %}
         env:
         - name: "K8S_HOST_URL"
           value: "{{ openshift_logging_fluentd_master_url }}"
@@ -107,6 +112,8 @@ spec:
             resourceFieldRef:
               containerName: "{{ daemonset_container_name }}"
               resource: limits.memory
+        - name: "USE_MUX_CLIENT"
+          value: "{{ openshift_logging_use_mux_client | default('false') | lower }}"
       volumes:
       - name: runlogjournal
         hostPath:
@@ -135,3 +142,8 @@ spec:
       - name: dockerdaemoncfg
         hostPath:
           path: /etc/docker
+{% if openshift_logging_use_mux_client | bool %}
+      - name: muxcerts
+        secret:
+          secretName: logging-mux
+{% endif %}