Added reboot apiserver
move ClearReboot to agent
Added comments
Merge pull request #728 from gabriel-samfira/reboot-api

WiP: Added apiserver endpoint for reboot

This is the second pull request for the reboot implementation. Please note that this is still a Work in Progress and a followup commit will be done for cleanup.

This branch depends on: https://github.com/juju/juju/pull/707