Race condition updating node_modules from dashboard

[garethbowen]

When updating an app, dashboard runs through a bunch of steps including deploying the app, updating settings, etc, before installing any node_modules.

However if the poll timer fires during this process it thinks the node_module isn't installed, and invokes the installation. This results in a module being installed before dashboard has finished installing the parent app.

This can cause the update to fail.

Pulling this over to the medic-os tree to test it out.