Revise the device deletion scenario

Instead of the Core removing the device right away, it was decided to have the following changes:

• On a device delete, the Core will wait until the adapter responds successfully before deleting the device. Note that during that period the device admin state will be DELETED.
• A force delete option will be introduced to the Voltha protos RPC. This action will force a deletion of the device, irrespective of the adapter response. This handles the case where the adapter is down.

While actions on a device in a DELETED state must be prohibited, there are some scenarios where the adapter will update the device operational/connection status during the deletion process. The device can be updated for these specific scenarios.