Fix Connection manager to retrieve inventory when is up

Fix Connection manager to retrieve inventory when is up

When ConnectionManager comes up, it's very much possible that may have
missed some inventory updates, so it needs to retrieve them to make
sure holes are covered, this is seen during integration test with the
stub protocol plugin, hence also make sure stub protocol plugin
provides the necessary hooks.

Change-Id: I41d5c71dd70aad909f7a75e0f596ec69a212400c
Signed-off-by: Giovanni Meo <gmeo@cisco.com>