CMUpdater: collapse statusbar when upgrading from notification

When clicking "Upgrade" from the notification action after
the updater successfully completes a download, the reboot
dialog would pop up underneat the statusbar, but it would
never be collapsed to let the user know.

This patch collapses the statusbar after the reboot
process begins.

Change-Id: I106b2118651702fd07afdfc8b4181139970a11a4
Signed-off-by: Roman Birg <roman@cyngn.com>