diffSystemAllocs -> diffSystemAllocsForNode, this function is only used
for diffing system allocations, but lacked awareness of eligible
nodes and the node ID that the allocation was going to be placed.
This change now ignores a change if its existing allocation is on an
ineligible node. For a new allocation, it also checks tainted and
ineligible nodes in the same function instead of nil-ing out the diff
after computation in diffSystemAllocs
cd00d6ded5