Clean up power state handling and fix voltage events

Seperate isPowerOn into two functions, one to set up the
match and one to poll the boolean. This way a dbus connection
object isn't needed in the sensor. Use this new function to
allow the ADCSensor to only signal threshold crosses if the
sensor is in the correct state.

Tested-by: Verified no SEL events for ADC sensors were created
during power cycling.

Change-Id: Ida800ab478b85ac2cb5976fa3471411c5d4bdc88
Signed-off-by: James Feist <james.feist@linux.intel.com>
10 files changed