lxd/main/daemon: Reworks cmdDaemon to use d.shutdownDoneCh and call d.Stop()
lxd/main/daemon: Reworks cmdDaemon to use d.shutdownDoneCh and call d.Stop()

 - Installs signal handlers before init so signals can be captured during init stage.
 - Also improves logging.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

hallyn/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd