From
https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/4498#note_397401883,
if you specify a relative path such as:

```
external_url 'http://gitlab.example.com/gitlab'
```

gitlab-shell doesn't have a way to pass the `/gitlab` to the host. For example, let's say we have:

```
gitlab_url: "http+unix://%2Fvar%2Fopt%2Fgitlab%2Fgitlab-workhorse%2Fsocket"
```

If we have `/gitlab` as the relative path, how do we specify what is the
UNIX socket path and what is the relative path? If we specify:

```
gitlab_url: "http+unix:///var/opt/gitlab/gitlab-workhorse.socket/gitlab
```

This is ambiguous. Is the socket in
`/var/opt/gitlab/gitlab-workhorse.socket/gitlab` or in
`/var/opt/gitlab/gitlab-workhorse.socket`?

To fix this, this merge request adds an optional
`gitlab_relative_url_root` config parameter:

```
gitlab_url: "http+unix://%2Fvar%2Fopt%2Fgitlab%2Fgitlab-workhorse%2Fsocket"
gitlab_relative_url_root: /gitlab
```

This is only used with UNIX domain sockets to disambiguate the socket
and base URL path. If `gitlab_url` uses `http://` or `https://`, then
`gitlab_relative_url_root` is ignored.

Relates to https://gitlab.com/gitlab-org/gitlab-shell/-/issues/476

This will make it easier to tie an SSH access request to Rails API and
Gitaly requests.

logrus fires a Goroutine to write logs, so the tests could fail if they
checked the event queue before the logrus have fired.  Since there isn't
an easy way to flush all outstanding hooks, we just retry every 100 ms
for up to a second for log to arrive in the queue.

Closes https://gitlab.com/gitlab-org/gitlab-shell/-/issues/450

Calling logrus hook.LastEntry() can lead to race conditions.  Use
AllEntries instead:
https://github.com/sirupsen/logrus/blob/60c74ad9be0d874af0ab0daef6ab07c5c5911f0d/hooks/test/test.go#L77

Closes https://gitlab.com/gitlab-org/gitlab-shell/-/issues/450

This would make it easier to filter the logs by status code.