Verify mac change on time stamp change

This test verifies that verification tokens with different time stamps do
not have the same MAC. This may not guarantee that the MAC is computed
correctly but it catches implementation that do not include the time
stamp in the mac.

It also checks that the MAC changes when both time stamp and challenge
changes.

Test: yes it is
Bug: 131859731
Bug: 132288466
Bug: 132287277
Change-Id: I85aa1d873eff46df7a66fc69bd61a031e6e6fbe0