Had the same issue with "Device Management is running" notification in the status bar for over an hour. Restart option from Power button selection didn't work. Finally did a hard restart (Press the down volume and power buttons at the same time for a few seconds until a message pops up saying your phone will restart - It's like pulling out the battery on other phones) and when the HTC One restarted, after a few moments I got the "Upgrade Successful to Android 4.3" message and the "Device Management is running" notice is gone.
Hope this works for you.