Monitor : handle inventory service offline

Using nameHasOwner and nameOwnerChanged D-Bus signals, a callback is
activated when inventory is started.

There are two primary modes for operation: Compatible Interfaces, the
inventory-detection callback will fail, however start() will be called a
second time after EntityManager starts and forces a reload of the proper
config for the machine type. Separately, if no EntityManager exists,
then the callback for Inventory-detection will succeed and use the
default configuration file.

To test: stop fan monitor and inventory services. start monitor, wait
10s, start Inventory, after about 15s you should see the online
detection.

Signed-off-by: Mike Capps <mikepcapps@gmail.com>
Change-Id: I289493a0aabb849abee8ce8de047513e94ee2219
3 files changed