CBQE-0: fix backgrounf thread tuq

Change-Id: I2cee0c89e47e4ccc9337f1f587e92bf7db7b2668
Reviewed-on: http://review.couchbase.org/29680
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>