consider a friendly error when no matching node.js engine found

[tjanczuk]

Currently when a node.js application requires a node.js engine version that is not satisfied by any version installed, arr.js will throw and bring the system down. Diagnostics is not easy (access logs.txt, or you can notice the condition using real time logs if you have them attach at the time of the post receive hook).

This is to disable this application and return a friendly 500 with description for requests targeting this application.