Don't always check controller status in controller_manager.live_controllers. (Too costly)
Don't always check controller status in controller_manager.live_controllers.
(Too costly)

User should instead first invoke check_controller_status if they want an
up-to-date list of live/dead controllers.

jmiserez/sts,ucb-sts/sts,jmiserez/sts,ucb-sts/sts