Add data_dir to emqx.conf (#2271)

* Add data_dir to emqx.conf

etc/emqx.conf

@@ -166,6 +166,11 @@ node.name = emqx@127.0.0.1
 ## Value: String
 node.cookie = emqxsecretcookie
 
+## Data dir for the node
+##
+## Value: Folder
+node.data_dir = {{ platform_data_dir }}
+
 ## Heartbeat monitoring of an Erlang runtime system. Comment the line to disable
 ## heartbeat, or set the value as 'on'
 ##

priv/emqx.schema

@@ -191,6 +191,10 @@ end}.
   {default, "emqxsecretcookie"}
 ]}.
 
+{mapping, "node.data_dir", "emqx.data_dir", [
+  {datatype, string}
+]}.
+
 %% @doc http://erlang.org/doc/man/heart.html
 {mapping, "node.heartbeat", "vm_args.-heart", [
   {datatype, flag},