Make Task state translatable.

The Task state None is currently not translated because it is the
literal value None.  Update to make sure it gets displayed as translated.
Also add in other missing task_states: 'reboot_pending', 'reboot_started',
'reboot_pending_hard', 'reboot_started_hard'

Change-Id: I4f9f8d22711896b2e9d39ef1bf5e803ca7bcbc0a
Closes-Bug: #1392848
Merge "Make Task state translatable."