Fix or disable offline tests

[LukasKorba]

3 offline tests are failing in the latest FFI branch changes. This is because viewing and spending keys are compared to some hardcoded values that were produced many years ago. The logic changed and we must update the hardcoded values.

[daira]

It is preferable to disable broken tests if they are not promptly fixed.

Broken test suites have an extremely high cost in terms of lack of confidence that test failures are meaningful (the "cry wolf" effect). That normally far outweighs the value of the particular tests that are broken.