random: Make the DRBG C-90 clean and use a flag string.

* random/random.h (struct gcry_drbg_test_vector): Rename "flags" to
"flagstr" and turn it into a string.
* random/random-drbg.c (drbg_test_pr, drbg_test_nopr): Replace use of
designated initializers.  Use a string for the flags.
(gcry_rngdrbg_cavs_test): Parse the flag string into a flag value.
(drbg_healthcheck_sanity): Ditto.

Libgcrypt needs to be build-able on C-90 only systems and thus we
can't use C-99 designated initializers. Because we have removed the
flag macros from the API we should not use them in the CAVS test code
either. Thus they are replaced by the flag string which also tests
the flag string parser.

• Signed-off-by: Werner Koch <wk@gnupg.org>