Add rockspecs directory for LuaRocks

In order to create lunatest-0.9.5-0.src.rock file and submit both that file and the rockspec to the LuaRocks project, please add the tag "v0.9.5" on master (I'm not sure tags are merged when merging a pull request).

I also resurrected the 0.9.1 and added 0.9.2 rockspecs for convenience, but with "lua ~> 5.1" instead of "lua >= 5.1" since thoses version are not compatible with Lua 5.2.