Rename -set-serial command to req
Rename -set-serial command to req

Previous OpenSSL versions used -set_serial, but master was using
-set-serial - so rename it back to the old version.

RT#4059

Reviewed-by: Richard Levitte <5fb523282dd7956571c80524edc2dccfa0bd8234@openssl.org>

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl