monitor: Don't create errors for missing sensors

Don't start the error timer (so no errors would be created) in the cases
where the tach sensor is being made nonfunctional because its value
can't be found on D-Bus, as that error indicates a problem with the fan
itself, which is fine.

Also don't check any power off actions in this case either so a running
system isn't turned off.

If no sensors at all are on D-Bus, that is already caught during a power
on.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: If5cd6d1d444be11b9666500db89b4bb82d7b282a
3 files changed