installing plugins - async state race condition

This can occur when we are installing plugins but we receive a user request to shutdown - if we unmount the plugingrid before the install finishes, we'll end up trying to call setState on a component (plugingrid) that isn't mounted

Start by tracing plugin installation and shutdown handling around the PluginGrid component, focusing on what happens when the component is unmounted before installation finishes. Reproduce the shutdown-during-install sequence and verify that no state update is attempted after PluginGrid is unmounted.

Written by the indexing model from the issue text.