SHDP-436 Adding counter measures for closing writers

- Added explicit `closed` flag in AbstractPartitionDataStoreWriter
  indicating a writer is closed and should not be used anymore.
  This now follows how writer should work after close() is called
  or context lifecycle stop has been initiated.
- Removed idlePoller result waiting in StoreObjectSupport
  which just never worked to let scheduled task to finish.
  That caused more trouble than it was supposed to fix.
- Few more smoke and context closing tests.