Add fluentd_binary and fluentd_version labels

In order to orchestrate a smooth migration of fluentd to newer
td-agent on CentOS x86_64, a label that points to fluentd binary
and version are needed.

Depends-On: https://review.opendev.org/677144/
Change-Id: Ie2257870d87c5b3a9b0572f8fd35085a3f95fedb

docker/fluentd/Dockerfile.j2

@@ -1,5 +1,10 @@
 FROM {{ namespace }}/{{ image_prefix }}base:{{ tag }}
 LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
+{% if base_package_type == 'rpm' or base_arch != 'x86_64' %}
+LABEL fluentd_version="0.12" fluentd_binary="fluentd"
+{% else %}
+LABEL fluentd_version="0.14" fluentd_binary="td-agent"
+{% endif %}
 
 {% block fluentd_header %}{% endblock %}