logdvmstate flush DB to disk

[Bushstar]

Summary

• CCustomCSView flushes its change map to a batch in underlying DB which then also needs to be flushed. This PR adds the flush to the underlying DB.
• Check arg before anything else.
• Add shutdown check to loop.

Implications

• Storage

  • [ ] Database reindex required
  • [ ] Database reindex optional
  • [ ] Database reindex not required
  • [x] None

• Consensus

  • [ ] Network upgrade required
  • [ ] Includes backward compatible changes
  • [ ] Includes consensus workarounds
  • [ ] Includes consensus refactors
  • [x] None