monitor: Start checking power off rules

In the system object, load the power off rules and start checking them.
It will check them in the following cases (if power is on):
* When the object is constructed
* When the JSON config is reloaded
* When fan presence or sensor functional state changes
* When the power state changes to on

When the power is turned off, it will cancel any running rules.

Previously, fan monitor was only designed to run with power on, and
there still may be more changes than just the ones added here to support
it always running.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I8be81612ae4997d7568678471ac0f6f854a0e758
2 files changed