The call to GET /allocation_candidates now accepts a 'member_of'
parameter, representing one or more aggregate UUIDs. If this parameter
is supplied, the allocation_candidates returned will be limited to those
with resource_providers that belong to at least one of the supplied
aggregates.
Blueprint: alloc-candidates-member-of
Change-Id: I5857e927a830914c96e040936804e322baccc24c