Pool Manager - Central/Storage Changes

domains table changes:
- Added 'ERROR' to status column
- Set status column default to 'PENDING'
- Added action column ('CREATE', 'DELETE', 'UPDATE', 'NONE')
  with a default of 'CREATE'

records table changes:
- Added 'ERROR' to status column
- Set status column default to 'PENDING'
- Added serial column with a default of 1
- Added action column ('CREATE', 'DELETE', 'UPDATE', 'NONE')
  with a default of 'CREATE'

Other modifications:
- Modified domain object to reflect new attribute (action)
- Modified record object to reflect new attributes (serial, action)
- Ensured central service continues to work by setting status of
  domain and record to 'ACTIVE'
- Added update_status method to central service

Change-Id: I893f8e7834de4c6ccf3ad587af65a7eee24415b3
Partially-implements: blueprint server-pools-service
Merge "Pool Manager - Central/Storage Changes"