truncate auth keys files to zero, but do not remove them (permissions are set at provisioning time)

lib/ssh.js

@@ -186,7 +186,7 @@ exports.configureProxy = function(host, behavior, cb) {
 
 exports.makePristine = function(host, cb) {
   var destination = 'ec2-user@' + host;
-  var rcmd = 'sudo rm ~root/.ssh/authorized_keys ~/.ssh/authorized_keys';
+  var rcmd = 'sudo truncate -s0 ~root/.ssh/authorized_keys ~/.ssh/authorized_keys';
   var args = ['-o', 'StrictHostKeyChecking no', destination, rcmd];
   passthrough(child_process.execFile(ssh, args, cb));
 };