Fix[mqb]: Handle orphan confirms

[dorjesinpo]

1. Do not break on orphan (auto) confirm
2. Do not send auto confirms if message refcount is 0

[678098]

Note that d_autoConfirms now keeps an invalid DataStoreRecordHandle.
What if that record handle never becomes valid (we never call FileBackedStorage::put) and we try to remove it in FileBackedStorage?

blazingmq/src/groups/mqb/mqbs/mqbs_filebackedstorage.cpp

Lines 1174 to 1184 in ea8e700

	void FileBackedStorage::clearSelection()
	{
	for (AutoConfirms::const_iterator it = d_autoConfirms.begin();
	it != d_autoConfirms.end();
	++it) {
	d_store_p->removeRecordRaw(it->d_confirmRecordHandle);
	}
	d_autoConfirms.clear();
	d_currentlyAutoConfirming = bmqt::MessageGUID();
	}

This might happen when all app subscriptions are negative (so all are auto confirmed) and we try to move to the next message.
See the integration test, I've posted a code update that causes broker to crash

[dorjesinpo]

selectForAutoConfirming should not call clearSelection
d_autoConfirms are used in two mutually exclusive ways - by RootQueueEngine and by replication.
The former never stores valid handles.

[dorjesinpo]

Fixes for IT failures:
#1175
#1193

[kaikulimu]

I only reviewed mqbs_filestore.cpp, and left one comment (as a reply to Evgenii's comment). The rest looks good.