tests: Add test to verify GOST 28147-89 against known results.

* tests/basic.c (check_gost28147_cipher): new test function.

Currently the only test executed against GOST 28147-89 cipher is a
basic cipher test: it checks that decoding of encoded text returns
the original plaintext. Add a function to verify the cipher against
test vectors.

• Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>