When doing a swapmod, nodes already reserved to the experiment are "moved"
(via update) to a holding reservation. Fine.  After assign runs, the old
nodes are moved back, but this time by an insert into the table, which
causes them to lose some fields that I do not want them to lose! This might
really mean that these fields do not belong in the reserved table, but I do
not want to ponder this right now. Instead I do another update bringing
them back into the original experiment.

I left comment indicating that this is under review (and why this commit is
seperate from the rest of the swapmod changes).