Detect the following problems:
 * Detect stale DB servers without corresponding Ganeti instances
 * Detect orphan Ganeti instances, without corresponding DB entries
 * Detect out-of-sync operstate for DB entries wrt to Ganeti instances
Fix them as follows:
 * Simulate server deletion for stale DB servers
 * Issue RAPI DeleteInstance() call for orphan Ganeti instances
 * Set operstate in DB as in Ganeti for out-of-sync DB servers

See ./manage.py reconcile --help for more info, refs #1021.