Slightly improve node status rendering
Slightly improve node status rendering

Summary:
'offline' is set to true or false when we know and unset when we don't.
Update the UI to reflect that.
Unknown state looks like this: {F343651}

Test Plan: Manual

Reviewers: nate

Reviewed By: nate

Subscribers: changesbot

Projects: #changes_ui

Differential Revision: https://tails.corp.dropbox.com/D178687

dropbox/changes,dropbox/changes,dropbox/changes,dropbox/changes