Update the way hard & soft reboots are displayed in task result

Currently the task result output does not distinguish between
nova hard and soft reboots. Following patch add this function.
The hard reboot will displayed as is nova.reboot_server and
soft reboot will be displayed as nova.soft_reboot_server.

Change-Id: I22ea2ddcf5c1a58697286ff292fb6a2a5fcaaee6
Closes-Bug:#1342138
Merge "Update the way hard & soft reboots are displayed in task result"