Bugfix: Don’t focus new cons when there is a fullscreen con (Thanks dothebart)

Also, remove the focus_it parameter from tree_open_con, it makes more sense to
call con_focus outside of the function.

src/cmdparse.y

@@ -403,7 +403,8 @@ open:
     TOK_OPEN
     {
         printf("opening new container\n");
-        Con *con = tree_open_con(NULL, true);
+        Con *con = tree_open_con(NULL);
+        con_focus(con);
         asprintf(&json_output, "{\"success\":true, \"id\":%ld}", (long int)con);
     }
     ;