Having this test fail with:
testtools.matchers._impl.MismatchError: 2 != 4
Doesn't really tell the developer what went wrong.
We can just compare the lists of devices directly so a mismatch
will show the devices that leaked in.
TrivialFix
Change-Id: Ic5a3b347bea7e5aa8a5caee5035568e5954f58dc