It's obviously necroposting, but I'd try my 2cents here anyways.
My advice is for those who ask how to install smth on Ubuntu.
There is another method to send shutdown messages without any dealings with Ubuntu by installing some app and configuring it.
APC does provide an image of completely tuned Ubuntu, ALREADY equipped with Web-interface.
Through this interface you'll be able to configure a lot of options, including shutdown commands to be sent to other networking devices in a case of power failure.
Hence a name of this linux machine: APC Network Shutdown.
All you need - is to deploy this image or appliance somewhere in your network at any ESXi host.
You may download PowerChute Network Shutdown v4.2 for Virtualization directly from APC site for free.