vts: Correct the parameters on strongbox

If GenerateKey() with user-provide key_blob, it needs to be specified in
the following begin() operations as well. Update the test case just to
take key_blob from private member instead of creating a local one.

Note:
- Remove redudent TAG_NO_AUTH_REQUIRED in DeviceUniqueAttestationTest

Change-Id: I81860294e1e7e01a57e66e08e75507a8292ec0c3