AUX provides an XML-RPC function for running the built in WordPress auto-upgrade using XML-RPC.
The XML-RPC method to call : aux.autoUpgradeWP
Parameters to pass:
XML-RPC must be enabled on your WordPres site. (Dashboard > Settings > Writing > Remote Publishing)
See https://github.com/karmadude/AUX for an example of using node.js to auto-upgrade multiple WordPress sites using AUX plugin.