tenant_id implies all_tenants for servers list in V3 API

Makes tenant_id imply all_tenants is also enabled unless
explicitly disabled when a request is made for a list of
servers. This only occurs if the requestor is an admin. The
change is only made for the V3 API as although this behavior is
more intuitive it is too late to change it for the V2 API.

Change-Id: Ia84e62c8dc80ac3a2f16aee3620af31987cce570
Partial-Bug: 1185290
Merge "tenant_id implies all_tenants for servers list in V3 API"