Fixed issues pointed out.

ref)
https://docs.gitlab.com/omnibus/settings/nginx.html#configuring-gitlab-trusted_proxies-and-the-nginx-real_ip-module

This reverts commit 47b5b441.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/17877#note_13488047

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/17877 .

This change adds 'defense in depth' against 'Host' HTTP header
injection. It affects normal users in the following way. Suppose your
GitLab server has IP address 1.2.3.4 and hostname gitlab.example.com.
Currently, if you enter 1.2.3.4 in your browser, you get redirected to
1.2.3.4/users/sign_in. After this change, you get redirected from
1.2.3.4 to gitlab.example.com/users/sign_in. This is because the
address you typed in the address bar of your browser ('1.2.3.4'),
which gets stored in the 'Host' header, is now being overwritten to
'gitlab.example.com' in NGINX.

In this change we also make NGINX clear the 'X-Forwarded-Host' header
because Ruby on Rails also uses that header the same wayas the 'Host'
header.

We think that for most GitLab servers this is the right behavior, and
if not then administrators can change this behavior themselves at the
NGINX level.

[ci skip]

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15398

Otherwise this might 'hide' problems
https://github.com/gitlabhq/gitlabhq/issues/10053#issuecomment-188919319

[ci skip]

It turns out that if we do not the declaration from
"location /" wins.

Limiting, if any, should happen in gitlab-workhorse.

- Offloads uploading to GitLab Workhorse
- Use /authorize request for fast uploading
- Added backup recipes for artifacts
- Support download acceleration using X-Sendfile

Users are allowed to supply namespace%2Fproject instead of a numeric ID

This change relies on changes in gitlab_git and gitlab-git-http-server.

Before this change NGINX would convert a chunked HTTP POST (e.g.
git push) into a HTTP 1.0 single large POST. This creates an
unnecessary delay, and it creates unnecessary memory pressure on
gitlab-git-http-server.

For the response ('proxy_buffering') I am less sure that NGINX 's
buffering behavior is harmful, but it still makes more sense to me
not to interfere with gitlab-git-http-server (and the Golang net/http
server).

https://gitlab.com/gitlab-org/gitlab-git-http-server

This change introduces the GITLAB_GRACK_AUTH_ONLY environment
variable. When set, Grack requests to GitLab will only respond with
the user's GL_ID (if the request is OK) or an error. This allows
gitlab-git-http-server to use the main GitLab application as an
authentication and authorization backend.

If we like how this works we should drop the GITLAB_GRACK_AUTH_ONLY
variable at some point in the future.

Revert "Merge branch 'go-get-workaround-nginx' of https://github.com/mattes/gitlabhq into mattes-go-get-workaround-nginx"

This reverts commit 51349ca3, reversing
changes made to b180476b.

We want to make users aware that the nginx default config will conflict
with the gitlab default_server conf file.

minor updates @ formatting changes to match other versions of file.
Unify formatting of
https://github.com/gitlabhq/gitlabhq/blob/master/lib/support/nginx/gitlab,
https://github.com/gitlabhq/gitlabhq/blob/master/lib/support/nginx/gitlab-ssl,
&
https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/gitlab/templates/default/nginx-gitlab-http.conf.erb

The current configuration sample files only enable IPv4 by default, making the
server inaccesible for many remote hosts (and an increasing amount every day).

Enable IPv4 and IPv6 by default. Older servers with no external IPv6
connectivity will not fail since they'll have a local-link IPv6 address to bind
to anyway.

Set's fail_timeout=0 as recommended by
http://unicorn.bogomips.org/Unicorn/Configurator.html#method-i-timeout
when Unicorn is running behind nginx.