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 <Gilles.Peskine@arm.com>

tests/ssl-opt.sh

@@ -564,8 +564,10 @@ run_test() {
         fi
     fi
 
-    # check server exit code
-    if [ $SRV_RET != 0 ]; then
+    # Check server exit code (only for Mbed TLS: GnuTLS and OpenSSL don't
+    # exit with status 0 when interrupted by a signal, and we don't really
+    # care anyway), in case e.g. the server reports a memory leak.
+    if [ $SRV_RET != 0 ] && is_polar "$SRV_CMD"; then
         fail "Server exited with status $SRV_RET"
         return
     fi