There are at least three sites online that cover this:
When I asked a similar question about Astana airport, my eventual solution was to use Foursquare - if people have checked in there, there's a good chance they had wifi, or may even mention it. I found the relevant page for the airport and voila - lots of mention of the wifi.
Also I nearly marked this as a dupe, but you may want to check out other free wifi links in a similar question on whether there are listed free wifi hospots around the world.