Add option to recover 2FA via SSH

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/3765

Allow users to recover their own account if they lose their 2FA device or recovery codes. 

## Questions/Concerns

- Does this look secure? I think it is but we need to make sure no one can spoof a username or something and disable two factor.

## Todo

- [x] Working code
- [x] Tests
- [x] GitLab merge requests (including documentation)

![Screen_Shot_2016-08-18_at_2.34.18_PM](/uploads/1ed00e93abdfc3b41187c021e4f9d4db/Screen_Shot_2016-08-18_at_2.34.18_PM.png)

See merge request !74

Sentinel Support

Sentinel connection parameters in `config.yml` file.

Fixes #29

See merge request !85

In order to use chomp! on the input later, we need to dup the ARGV input string for keys

Also updated the gitlab_key tests to freeze the ARGV variables.

Fixes https://gitlab.com/gitlab-org/gitlab-shell/issues/56

See merge request !84

Show Merge request link after pushing if new brach

This is part of implementation for issue https://gitlab.com/gitlab-org/gitlab-ce/issues/18266

See merge request !77

update spec

different text for new and existing merge request

update spec

fix style

switch order of messages

enhance message appearance

remove extra spaces

Also updated the gitlab_key tests to freeze the ARGV variables.

Update the keys permission check to open the file in write mode.

That way the file is created if it does not exist.

This will help simplify the check being running from omnibus. Currently we create the authorized_keys, file in omnibus. We want to instead have omnibus call check-permissions as the git user, to get around nfs root_squash issues with the authorized_keys file.

See merge request !83

That way the file is created if it does not exist.

Defense in depth for authorized_keys lines

Validate the key_id and public_key inputs when rendering the actual
'line' we append to authorized_keys. Although these inputs are either
trusted (key_id) or validated earlier (public_key) it does not hurt to
take a little extra care that we do not write unintended data to the
authorized_keys file.

See merge request !82

Small improvements

- refactor GitlabKey away
- fix Redis check output

See merge request !81

It is not nice to have both 'GitlabKeys' and 'GitlabKey'. We also do
not need GitlabKey to be a class when it has no state.

Improve authorized_keys check

The old check only looked if authorized_keys exists. With this change, we look
whether we can actually open the file for reading and writing. When this fails
we try to print useful diagnostic information.

See merge request !79

The old check only looked if authorized_keys exists. With this change, we look
whether we can actually open the file for reading and writing. When this fails
we try to print useful diagnostic information.

Manage authorized_keys permissions continuously

We can lazily create authorized_keys and set its permissions. This
adds negligible overhead and it allows us to remove a setup step from
GitLab both on source and in omnibus-gitlab.

See merge request !78

We can lazily create authorized_keys and set its permissions. This
adds negligible overhead and it allows us to remove a setup step from
GitLab both on source and in omnibus-gitlab.

Add command to move repositories between repository storages

Necessary for https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/533

/cc @pcarranza 

See merge request !71

Track ongoing pushes and reject mv-storage commands if there are push running (after waiting some time)

Merge branch '51-gitlab-project-s-fork_project-command-doesn-t-work-if-the-project-is-being-forked-to-another-storage' into 'master'

Allow gitlab-project's fork-project command to fork projects between different repository storages

Closes #51

See merge request !75

Unset GL_ID and GL_PROTOCOL immediately

Neither other code executing in the hook process nor subprocesses of
the hook process need access to the GL_ID / GL_PROTOCOL variables so
we can just unset them the moment we fetch them.

See merge request !73