Backport(v1.16) papertrail: add CRI parser fallback (#1541) (#1560)

Closes: #1537

When parser is replaced to CRI parser in tail_container_parse.conf,
parsed output stored into message not log.
As a result, blank message will be omitted.

Signed-off-by: Kentaro Hayashi <[email protected]>

Author: kenhys

templates/conf/kubernetes.conf.erb

@@ -61,7 +61,7 @@
     program ${record["kubernetes"]["container_name"]}
     severity info
     facility local0
-    message ${record['log']}
+    message ${record['log'] || record['message']}
   </record>
 </filter>
 <% end %>