add file exists checking in my_uuid

scripts/lib/commons.lua

@@ -0,0 +1,13 @@
+local _M = {}
+
+function _M.file_exists(name)
+    local f = io.open(name, "r")
+    if f ~= nil then
+        io.close(f)
+        return true
+    else
+        return false
+    end
+end
+
+return _M