Fix error discrepancy.

We can't rename ssleay_rand_bytes to md_rand_bytes_lock as this will cause
an error code discrepancy. Instead keep ssleay_rand_bytes and add an
extra parameter: since ssleay_rand_bytes is not part of the public API
this wont cause any binary compatibility issues.
Reviewed-by: Kurt Roeckx <kurt@openssl.org >
(cherry picked from commit 8068a675a7d1a657c54546f24e673e59e6707f03)