Add sticky disk to service template

nomad/service.nomad

@@ -3,6 +3,7 @@
 # image = string*
 # service_port = int
 # ingress = bool
+# sticky_disk = bool
 # args = json(list[str])
 # resources = dict(cpu = int, mem = int)
 # templates = json(list(dict(
@@ -36,6 +37,13 @@ job "[[.name]]" {
       [[ end ]]
     }
 
+    [[ if default false .sticky_disk ]]
+    ephemeral_disk {
+      migrate = true
+      sticky = true
+    }
+    [[ end ]]
+
     [[ if not (empty .service_port) ]]
     service {
       name = "[[.name | replace "_" "-"]]"