IPAllocationPool has relation to IPAvailabilityRange which is setup to
load eagerly. Eager loading is implemented with left outer join which is
incompatible with with_lockmode('update') on postgresql.
The fix redefines eager loading with options(joinedload) making it use
inner join.
fixes bug 1215350
Change-Id: I148d37f2a1c2a340327d36c240eb8173aee9219a