Add etcd_blkio_weight var (#1690)

roles/etcd/templates/etcd.j2

@@ -12,6 +12,9 @@
   {% if etcd_cpu_limit is defined %}
   --cpu-shares={{ etcd_cpu_limit|regex_replace('m', '') }} \
   {% endif %}
+  {% if etcd_blkio_weight is defined %}
+  --blkio-weight={{ etcd_blkio_weight }} \
+  {% endif %}
   --name={{ etcd_member_name | default("etcd") }} \
   {{ etcd_image_repo }}:{{ etcd_image_tag }} \
   {% if etcd_after_v3 %}