Comment 6 for bug 1516144

I'm not sure if this is *the* problem, but I can see *a* problem with the current unit assigner code in state.

Unit.assignToMachineOps calls the removeStagedAssignmentOp method to get an op that removes the unit-assignment doc. Unit.assignToNewMachine does not do that. The unit assigner changes have changed the behaviour of unit-to-machine assignment, which has uncovered another issue with the assignToNewMachine method -- it doesn't add storage attachments to the new machine.

I'm not entirely sure how this would have triggered, but if the machine agent restarts it's going to see old unit assignment docs in the collection still, and try to assign them again.