SCAN for inventory changes

Periodic scanning for inventory changes is needed, as classic currently does in provisiond.  Note that scanning typically runs about once per week.

The process needs to do the following:

• Read the requisitions
• Detect inventory based on the contents of the requisitions
• Update the inventory in the DB (e.g. add nodes, interfaces, etc) based on the results of the detection
• Send update events

Updates based on the results of scanning are directly reflected in the database.