daemon: Make sure all the traverse children are terminated if traverse times out

daemon: Make sure all the traverse children are terminated if traverse times out

When traverse times out, callback function is called with key and data set to
tdb_null.  This is also the way to signal end of traverse.  So if the traverse
times out, callback function treats it as traverse ended and frees state without
calling the destructor.

Keep track if the traverse timed out, so callback function can take appropriate
action for traverse timeout and traverse end.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Cherry-pick-from: 35da9a7c2a0f5e54e61588c3c3455f06ebc66822