Fix bio_enc_test

There was a block of code at the start that used the Camellia cipher. The
original idea behind this was to fill the buffer with non-zero data so that
oversteps can be detected. However this block failed when using no-camellia.
This has been replaced with a RAND_bytes() call.

I also updated the the CTR test section, since it seems to be using a CBC
cipher instead of a CTR cipher.

Reviewed-by: Andy Polyakov <appro@openssl.org>