Enable X-Auth-Project flag in HTTP headers

This also enables adding all_projects=true as part of the query string

This will set the "all_tenants" flag in the context, and does a policy
check to ensure the all_tenants is authorised

Closes-Bug: 1319112
Change-Id: Ic8c9a65a61784e0e08fa48961b7d6154d05fb11c
Merge "Enable X-Auth-Project flag in HTTP headers"