Add compression tests

Check whether we negotiate compression in various scenarios.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2814)
diff --git a/test/handshake_helper.c b/test/handshake_helper.c
index 88f6aec..99b6ad1 100644
--- a/test/handshake_helper.c
+++ b/test/handshake_helper.c
@@ -1207,6 +1207,9 @@
         ret->session_ticket = SSL_TEST_SESSION_TICKET_NO;
     else
         ret->session_ticket = SSL_TEST_SESSION_TICKET_YES;
+    ret->compression = (SSL_get_current_compression(client.ssl) == NULL)
+                       ? SSL_TEST_COMPRESSION_NO
+                       : SSL_TEST_COMPRESSION_YES;
     ret->session_ticket_do_not_call = server_ex_data.session_ticket_do_not_call;
 
 #ifndef OPENSSL_NO_NEXTPROTONEG