scripts: add functions need_one_of and need_array_of to check_site_lib.lua

need_one_of(varname, array, required) checks weather the value of the specified variable is part of given array.
need_array_of(varname, array, required) is similar to need_one_of() but assume that varname points to an array.

scripts/check_site_lib.lua

@@ -7,6 +7,27 @@ local function loadvar(varname)
    end
 end
 
+local function array_to_string(array)
+   local string = ''
+   for _, v in ipairs(array) do
+      if #string >= 1 then
+         string = string .. ', '
+      end
+      string = string .. v
+   end
+   return '[' .. string .. ']'
+end
+
+local function assert_one_of(var, array, msg)
+   for _, v in ipairs(array) do
+      if v == var then
+         return true
+      end
+   end
+
+   error(msg)
+end
+
 local function assert_type(var, t, msg)
    assert(type(var) == t, msg)
 end
@@ -99,7 +120,25 @@ function need_table(varname, subcheck, required)
    return var
 end
 
+function need_one_of(varname, array, required)
+   local var = loadvar(varname)
+
+   if required == false and var == nil then
+      return nil
+   end
+
+   assert_one_of(var, array, "site.conf error: expected `" .. varname .. "' to be one of given array: " .. array_to_string(array))
+
+   return var
+end
+
 function need_string_array(varname, required)
    return assert(pcall(need_array, varname, function(e) assert_type(e, 'string') end, required),
 		 "site.conf error: expected `" .. varname .. "' to be a string array")
 end
+
+function need_array_of(varname, array, required)
+   local ok, var = pcall(need_array, varname, function(e) assert_one_of(e, array) end,required)
+   assert(ok, "site.conf error: expected `" .. varname .. "' to be a subset of given array: " .. array_to_string(array))
+   return var
+end