clean up tmp files from npm

[mandric]

Using npm 2.5.1 we observe that files are left in /tmp/ after installation. This can cause the disk to fill up if you do many installations. We probably need to do some manual cleanup of npm or pass the right parameters to the library so it cleans up properly. After an install completes you will noticed a /tmp/npm-$hash directory, these should be removed after a successful install.