Recover from POWERING-* state on compute manager start-up

If a compute manager is stopped / fails during POWERING-ON or
POWERING-OFF operations then the instance will be left stuck in
a transitional task_state.

This change handles both these states by simply either retriggering
the power on or power off request on start-up of the compute manager.
If the operation had previously completed then retrying will
essentially be a no-op so it is safe to handle instances in this
state in this way.

Closes bug: #1304333
Change-Id: I262be6b13a764bc1355be34cdc0180e8e87f260b
Merge "Recover from POWERING-* state on compute manager start-up"