Disable all 'close' event handlers before disconnecting in NodeConnection-test.js

There is an unhandled exception triggered by the final test in `NodeConnection-test.js`. It's caused by a `"close"` event handler that expects a reconnection promise which does not exist. Reconnection promises are provided for connections that are set to auto-reconnect, but **not** when the connection is explicitly closed with `disconnect()`. This pull request disables `"close"` event handlers before disconnecting all of the connections opened for testing in the `afterEach` handler.

Assigning to @dangoor. Should be easy to verify.