rgw: fix build with Lua 5.5

rgw: fix build with Lua 5.5

Lua 5.5 added a `seed` parameter to `lua_newstate()`. Use a
preprocessor conditional to pass the extra argument when building
against Lua >= 5.5.

Since we require Lua >= 5.3 in src/CMakeLists.txt, we need to be
compatible with Lua 5.5 as well.

See https://www.lua.org/manual/5.5/manual.html#lua_newstate

Signed-off-by: Kefu Chai <k.chai@proxmox.com>