bug1037171 Ensure find my device cancellation (or error) does not result...

bug1037171 Ensure find my device cancellation (or error) does not result in FMD becoming enabled on subsequent FxA login r=mgoodwin
nit: I would prefer not to leave the bug id in the test name as the use case here is not complex. The test case could been seen as a part of the basic tests of the feature.