ssl-opt.sh: Only check the server exit for Mbed TLS
ssl-opt.sh: Only check the server exit for Mbed TLS

We care about the exit code of our server, for example if it's
reporting a memory leak after having otherwise executed correctly.

We don't care about the exit code of the servers we're using for
interoperability testing (openssl s_server, gnutls-serv). We assume
that they're working correctly anyway, and they return 1 (gnutls-serv)
or die by the signal handle the signal (openssl) when killed by a
signal.

Signed-off-by: Gilles Peskine <f805f64266d288fc5467baa7be6cd0ff366f477b@arm.com>

NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls