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.
SSL: misplaced space in debug message.
Bigger iovec buffer in ngx_readv_chain().

This helps to reduce likelyhood of memory allocations in ngx_readv_chain(),
which are known to lead to noticeable effects in some cases, see
http://mailman.nginx.org/pipermail/nginx/2014-July/044512.html.