Remove the update-head command since GitLab doesn't use it anymore

It looks like we tend to remove commands that are not used by GitLab anymore (see gitlab-org/gitlab-shell!26) and the `update-head` command will soon be in that case (see https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3705), so I think we should remove it from here too.

Note: I'm setting this as a WIP to ensure this doesn't get merged since the GitLab MR is not merged at that moment.

See merge request !51

Signed-off-by: Rémy Coutable <remy@rymai.me>

Revert "Remove unused #list_remote_tags"

This reverts commit f5e87590 because `#list_remote_tags` is still used by EE:https://gitlab.com/gitlab-org/gitlab-ee/blob/2c364a79ee110a3adf49d6bd30be985ed13c3ec5/lib/gitlab/backend/shell.rb#L45.

/cc @razer6 

See merge request !56

This reverts commit f5e87590.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Update post receive worker so it logs a unique JID in sidekiq

Taken from !50.

Instead of

```
2016-04-14T03:07:32.373Z 5285 TID-osycgmlyo PostReceive JID- INFO: start
2016-04-14T03:07:32.374Z 5285 TID-osycgmlyo PostReceive JID- INFO: arguments: [...]
2016-04-14T03:07:32.534Z 5285 TID-osycgmlyo PostReceive JID- INFO: done: 0.161 sec
```

Have this log

```
2016-04-14T03:07:32.373Z 5285 TID-osycgmlyo PostReceive JID-54b0b2f6616cae37e3e87f8a INFO: start
2016-04-14T03:07:32.374Z 5285 TID-osycgmlyo PostReceive JID-54b0b2f6616cae37e3e87f8a INFO: arguments: [...]
2016-04-14T03:07:32.534Z 5285 TID-osycgmlyo PostReceive JID-54b0b2f6616cae37e3e87f8a INFO: done: 0.161 sec
```


This way sidekiq can Log a unique JID in the sidekiq.log for PostReceive.
So when parsing the logs (with logstash for example) you know it belongs to that unique job.

This puts the logs in a uniform manner like the other workers that are pushed to redis (which do have a JID)
For example the ProjectWebHookWorker

```
2016-04-14T03:13:07.917Z 5285 TID-osycsh7z0 ProjectWebHookWorker JID-800085fb3cf7241fdeecc6ec INFO: start
2016-04-14T03:13:07.918Z 5285 TID-osycsh7z0 ProjectWebHookWorker JID-800085fb3cf7241fdeecc6ec INFO: arguments: [...]
2016-04-14T03:13:12.500Z 5285 TID-osycsh7z0 ProjectWebHookWorker JID-800085fb3cf7241fdeecc6ec INFO: done: 4.583 sec
```


See merge request !55

Remove branch functionality

The branch functionality is already replaced with rugged inside GitLab

See merge request !52

Remove rm-tag command

Not needed anymore because gitlab-org/gitlab-ce!3748 switched the functionality to rugged.

See merge request !54

Remove unused #list_remote_tags

This function is not used anymore inside GitLab.

See merge request !53

Prune during 'git gc' after all

See merge request !48

This reverts commit 1ca8a44f.

Never pruning loose objects at all is not really a solution for
anything, and it causes annoying `git gc --auto` warnings.

Add new command to list tags from a remote repo.

The output of the `git ls-remote` command is written to the STDOUT so
the client can read and parse the list of tags. If there is an error it's
also written to STDOUT.

Closes #39 

See merge request !47

The output of the `git ls-remote` command is written to the STDOUT so
the client can read and parse the list of tags. If there is an error it's
also written to STDOUT.

[ci skip]

Add the ability to fetch remote repo without tags.

When fetching remote repo with tags the new remote tags are mixed in
with the local tags (all tags are saved under refs/tags), this affects
the UI of the Project given that we're showing up tags of a remote repo.

REF: https://gitlab.com/gitlab-org/gitlab-ee/issues/116

See merge request !46

When fetching remote repo with tags the new remote tags are mixed in
with the local tags (all tags are saved under refs/tags), this affects
the UI of the Project given that we're showing up tags of a remote repo.

Use ssh key internal api to build the authorized-keys command on openssh 6.9

See merge request !42

This provides the integration point to the internal API to get the
ssh key from the internal API.

Add new required commands to update remote mirrors

Closes gitlab-org/gitlab-ee#116

See merge request !43

Fix git-annex issue when using SSH on a custom port

Easiest thing here is to use the full repo path on the server side.

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/166

See merge request !45