This patch modifies Nova objects that will allow Destination object to
store list of forbidden aggregates that placement should ignore in
'GET /allocation_candidates' API at microversion 1.32, including the
code to generate the placement querystring syntax from them.
Change-Id: Ic2bcee40b41c97170a8603b27b935113f0633de7
Implements: blueprint placement-req-filter-forbidden-aggregates
3c8af001d5