Fixes incorrect exchange lock in fake driver

The exchanges lock in the fake driver was being disregarded,
probably due to a typo.

Closes-Bug: #1342088
Change-Id: I45261fce501a867b9253112e1608b14ed5afea26
(cherry picked from commit 1cc3e5d866ee51b7cd542e8a00721329b2bbed3c)
Merge "Fixes incorrect exchange lock in fake driver" into stable/icehouse