All types of the DRBG (CTR, HMAC, Hash) are covered with test vectors.
In addition, all permutations of use cases of the DRBG are covered:

        * with and without predition resistance
        * with and without additional information string
        * with and without personalization string

As the DRBG implementation is agnositc of the specific backend cipher,
only test vectors for one specific backend cipher is used. For example:
the Hash DRBG uses the same code paths irrespectively of using SHA-256
or SHA-512. Thus, the test vectors for SHA-256 cover the testing of all
DRBG code paths of SHA-512.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>