Serialize the notification payload in json

When a notification payload is passed to the oslo.messaging the
payload must be correctly serialized.

This change encode the payload into json as the old rpc did.

Closes bug: #1279881

Change-Id: I99fc2a4b0e0146c9faa6abeddbd15cb24169e024
VMware: add a test for driver capabilities

Check the values of the driver capability flags.

Change-Id: If1b18c0a48efd90d6b3c113f73457c1d0f552bb1
Merge "Serialize the notification payload in json"
Merge "VMware: add a test for driver capabilities"