Introduced strong synchronization

- Strong synchronization across listeners with Locks and synchronizaed
- Strong synchronization in checked future callback with semaphores
- Fixed several logs
- Added more javadocs
- Removed busy wait form SfcDataStoreAPIs

Change-Id: I4d58ea8c13be61b1fc6aac96e29400939a661b5c
Signed-off-by: Reinaldo Penno <rapenno@gmail.com>