Fix typo in prometheus-node-exporter restart handler

Change-Id: Ib05569a08e2fe21dae31cdacad3b622d17cb5db3

ansible/roles/prometheus/handlers/main.yml

@@ -24,7 +24,7 @@
     common_options: "{{ docker_common_options }}"
     name: "{{ service.container_name }}"
     image: "{{ service.image }}"
-    pid_mode: "{{ service.pid_mode | default(emit) }}"
+    pid_mode: "{{ service.pid_mode | default(omit) }}"
     volumes: "{{ service.volumes }}"
     dimensions: "{{ service.dimensions }}"
   when: