Upstream: SSL handshake timeouts.

Timeout may not be set on an upstream connection when we call
ngx_ssl_handshake() in ngx_http_upstream_ssl_init_connection(),
so make sure to arm it if it's not set.

Based on a patch by Yichun Zhang.
diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 58edc62..18b04f7 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -1393,6 +1393,11 @@
     rc = ngx_ssl_handshake(c);
 
     if (rc == NGX_AGAIN) {
+
+        if (!c->write->timer_set) {
+            ngx_add_timer(c->write, u->conf->connect_timeout);
+        }
+
         c->ssl->handler = ngx_http_upstream_ssl_handshake;
         return;
     }