[shimV2] Minor refactoring changes

[rawahars]

Following changes needs to be made as part of a small refactor-

• Change VPCI and Network controller to conform to design of other controllers
  • Eliminate unsupported files.
  • Use common interface for LCOW and WCOW implementation
• Introduce StateInvalid in SCSI controller similar to Plan9 controller
• All the V2 code paths should have lcow or wcow tags
• Enable tests and builds for V2 shim
• Disable vpmem with V2 shim
• Reduce logs in the shim
• Once all the PRs are added, ensure that comments, logs and error formats are same