Tests: add file/dir existence check utility function
Tests: add file/dir existence check utility function

Use it instead of os.rename(path, path).

robooo/luarocks,robooo/luarocks,xpol/luarocks,xpol/luarocks,tarantool/luarocks,xpol/luainstaller,robooo/luarocks,tarantool/luarocks,tarantool/luarocks,keplerproject/luarocks,luarocks/luarocks,xpol/luavm,xpol/luainstaller,xpol/luavm,xpol/luarocks,xpol/luavm,luarocks/luarocks,robooo/luarocks,xpol/luavm,luarocks/luarocks,xpol/luainstaller,xpol/luavm,xpol/luainstaller,keplerproject/luarocks,keplerproject/luarocks,xpol/luarocks,keplerproject/luarocks