MINOR: ssl/cli: 'show ssl cert'displays the issuer in the chain

For each certificate in the chain, displays the issuer, so it's easy to
know if the chain is right.

Also rename "Chain" to "Chain Subject".

Example:

  Chain Subject: /C=FR/ST=Paris/O=HAProxy Test Intermediate CA 2/CN=ca2.haproxy.local
  Chain Issuer: /C=FR/ST=Paris/O=HAProxy Test Intermediate CA 1/CN=ca1.haproxy.local
  Chain Subject: /C=FR/ST=Paris/O=HAProxy Test Intermediate CA 1/CN=ca1.haproxy.local
  Chain Issuer: /C=FR/ST=Paris/O=HAProxy Test Root CA/CN=root.haproxy.local
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index 222a206..94fff9b 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -10723,7 +10723,7 @@
 		for (i = 0; i < sk_X509_num(ckchs->ckch->chain); i++) {
 			X509 *ca = sk_X509_value(ckchs->ckch->chain, i);
 
-			chunk_appendf(out, "Chain: ");
+			chunk_appendf(out, "Chain Subject: ");
 			if ((name = X509_get_subject_name(ca)) == NULL)
 				goto end;
 			if ((ssl_sock_get_dn_oneline(name, tmp)) == -1)
@@ -10731,6 +10731,13 @@
 			*(tmp->area + tmp->data) = '\0';
 			chunk_appendf(out, "%s\n", tmp->area);
 
+			chunk_appendf(out, "Chain Issuer: ");
+			if ((name = X509_get_issuer_name(ca)) == NULL)
+				goto end;
+			if ((ssl_sock_get_dn_oneline(name, tmp)) == -1)
+				goto end;
+			*(tmp->area + tmp->data) = '\0';
+			chunk_appendf(out, "%s\n", tmp->area);
 		}
 	}