Using ConsoleHelper::write_stderr

.write_stderr
.format_for_stderr

print_warnings is now using that method in order to print a large
formatted warning message, so renaming the method to be less tied to
the broadcast message functionality.

Warnings are printed using the same method that prints broadcast
messages. This ensures that whatever warnings are returned will be
displayed correctly.

This allows gitlab-shell to be called with an argument of the format
`key-123` or `username-name`.

When called in this way, `gitlab-shell` will call the GitLab internal
API. If the API responds with user information, it will print a
welcome message including the username.

If the API responds with a successful but empty response, gitlab-shell
will print a welcome message for an anonymous user.

If the API response includes an error message in JSON, this message
will be printed to stderr.

If the API call fails, an error message including the status code will
be printed to stderr.

This will enable us to track the human-readable project path with SSH
access in gitlab-shell. Currently the Gitaly logs will only show the
hashed storage and gl_repository path (e.g. project-1234).

When SSH_CONNECTION is not set, we don't fall back to ruby, but
instead fail directly in go writing the error to stderr.

This adds the possibility to enable features for GitLab shell.

The first feature being recognized is "Discover": It's the command
that is executed when running `ssh git@gitlab.example.com` and is
called without a command.

The gitlab key id or username is already parsed from the command line
arguments.

Currently we only support communicating with GitLab-rails using unix
sockets. So features will not be enabled if the GitLab-url is using a
different protocol. The url for this read from the config yaml.

Pending ruby-specs have been added for the gitlab-shell command.

Refactor to have separate command packages

push_opts[] is named as such so that it becomes an array in the
GitLab internal Grape::API params hash. If it were named push_opts, only
the final (scalar) push_opts parameter would be present.

Also update specs to include push_opts parameter:
- gitlab_post_receive_spec
- gitlab_net_spec for the internal API change

This module is responsible for converting the GIT_PUSH_OPTION_*
environment variables into an array.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/18667

This reverts merge request !257

As of 7eb45672, NamesHelper is no longer used.

Operation is either upload or download

This also cleans up the output from the tests as previously, Base64 encoded output was printed.

Ensure text/plain & text/html content typs are handled and add missing specs for handled HTTP status codes

GitlabConfig spec was relying upon real config.yml

After the cleanup in https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/231
gitlab-shell mishandled the non 200 response codes. This commit removes
another few lines of codes, which fixes this. Also now we test against
this case through mocking.

Fixes https://gitlab.com/gitlab-org/gitlab-shell/issues/152

Given the gitaly-* now proxy the data from the client to the Gitaly
server, the environment variables aren't used. Therefor we don't have to
set them either. Only exception to the rule, is the GITALY_TOKEN.

These changes also remove the `GIT_TRACE` options, introduced by
192e2bd3.

Part of: https://gitlab.com/gitlab-org/gitaly/issues/1300

All shell access goes through Gitaly, so dead code paths exist to
support the legacy way too.

This change mostly removes the dead code from `#process_cmd`.

The internal api returns '/' from gitlab, since
`8fad07383ada021fc995294fd0fe0f77fe37da35` from GitLab CE. To clean up
later, https://gitlab.com/gitlab-org/gitlab-shell/issues/135 was
created.

This change closes that issue, making it possible to remove the field
from the response on GitLab-CE too. Given the Rails app always returns
`/` as the repository_path, the associated checks are basically a noop
too. The tests are updated and at times look a little fishy, but those
are testing code that is to be removed in another MR.

Closes https://gitlab.com/gitlab-org/gitlab-shell/issues/135