Avoid nullpointer exception on starting up the TopologyProvider and the InventorReadA...

Avoid nullpointer exception on starting up the TopologyProvider and the InventorReadAdapter

The TopologyProvider and InventoryAndReadAdapter are Felix services which get started when all it's
dependencies are resolved (that is their start method gets called). The MD-SAL DataProviderService is not
or cannot be injected into them and so when start is called and the dataProviderService is used it throws an NPE

To fix this I simply moved most of the startup code into a separate method which I then call from the ComponentActivator
instead of start

Change-Id: Ia6f0b6cebd38f4af7f03c9da8a5e26e05c13f664
Signed-off-by: Moiz Raja <moraja@cisco.com>