Add verification REST service to Barbican

Add initial REST resources and simple business logic (i.e. always return
'True' for the is-valid query). Add unit testing and verify works with
REST client.

Change-Id: Iccb3b2babe7be1907acae297ae8b479c3c3a247f
Implements: blueprint api-add-verification
Merge "Add verification REST service to Barbican"