Make X-Project-ID a required header

We decided to make X-Project-ID a required header for every request. If
not present, a 400 error should be raised.

Partially-Implements: blueprint api-v1.1-header-changes
Change-Id: I6c6c21585e9a738ff7c0f74ce6a284229ebec2aa
Merge "Make X-Project-ID a required header"