Support oauth for calls from VNFM to VNFM adapter

strong textSOL003 specification allows oauth token based authentication between the client and server. 

This story will enable using oauth from the VNFM to the VNFM adapter for grant requests and notifications.

The VNFM simulator will also be updated to use the credentials passed in the subscription request to request a token from the adapter which will then be used in grant requests to the adapter.

The username/password accepted by the adapter for token requests will be configurable.

As per SOL003 spec, basic auth will continue to be accepted for notifications into the adapter