Batching API batch retrieval changes

Allows one last batch of fixes, if available, be retrieved by HIDL
client after stop() is called. Also, if flush() is called, service
end will always report something, empty if no more fixes in the
batch.

Change-Id: Ie4d196b2ba3b55cb7dd1a7510a9d887f0b997281
CRs-fixed: 2870223
3 files changed