Use 'length' filter on remote plugins conditional

tasks/plugins.yml

@@ -14,7 +14,7 @@
     shell: sensu-install -p {{ item }}
     with_items: sensu_remote_plugins
     changed_when: false
-    when: sensu_remote_plugins > 0
+    when: sensu_remote_plugins|length > 0
 
   - name: Register available checks
     local_action: command ls {{ static_data_store }}/sensu/checks