Backport some (should be safe) changes from google nginx

[CarterLi]

Because of the large size, I put them into my gist: https://gist.github.com/CarterLi/f6e21d4749984a255edc7b358b44bf58

For now, there are 3 patches ported:

1. Use openssl md5 / sha1
2. Add $upstream_bytes_sent variable.
3. Add "proxy_ssl_alpn" directive

All 3 patches are generated from the clean nginx 1.15.0 code base and can be applied together with sslconfig nginx.patch

[kn007]

Interesting, look great.
Thank you

[kevin25]

@kn007 @CarterLi Have you tested it with Nginx 1.15.2?

[CarterLi]

Only openssl md5 / sha1 @kevin25

[Harvester57]

I concur, the OpenSSL MD5/SHA1 patch applies nicely on Nginx 1.15.2