Add check for OpenSSL entropy status

By checking for this explicitly, the errors (SSLEAY_RAND_BYTES, “PRNG
not seeded”) will happen in the start-up phase of the daemon and not
only when executing remote procedure calls.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>