Verify state of device before running tests.

We see some failures that would be explained by previous test runs leaving
the device in a bad state. Add some asserts to catch this case and fail
early.

Bug: 170428909
Bug: 169987505
Test: cd cd cts/tests/signature/; atest
Change-Id: I9f09de789b1a6290d96a8e51cea67306287c660b
4 files changed