[VOL-1614] Device Management update in the Core

This commit went over the device management of devices in the Core
and made the following changes:
1) Update the device state machine to not remove logical
device or ports when a device is disabled.
2) Fix some issues around device deletion
3) Add additional APIs between the Core and Adapters to handle
the scenarios of enable/disable/delete a device
4) Update the simulated Adapters to handle disable/reenable/delete
5) Add a new set of tests for teh device state machine.

Change-Id: Ib2be87ec011762d5315a6d54581a87c1891e92be
diff --git a/adapters/iAdapter.go b/adapters/iAdapter.go
index a1dfa16..017082d 100644
--- a/adapters/iAdapter.go
+++ b/adapters/iAdapter.go
@@ -33,7 +33,7 @@
 	Reenable_device(device *voltha.Device) error
 	Reboot_device(device *voltha.Device) error
 	Self_test_device(device *voltha.Device) error
-	Gelete_device(device *voltha.Device) error
+	Delete_device(device *voltha.Device) error
 	Get_device_details(device *voltha.Device) error
 	Update_flows_bulk(device *voltha.Device, flows *voltha.Flows, groups *voltha.FlowGroups) error
 	Update_flows_incrementally(device *voltha.Device, flows *openflow_13.FlowChanges, groups *openflow_13.FlowGroupChanges) error