Tweak to support really big merge requests

Related to:

https://gitlab.com/gitlab-org/gitlab-ce/issues/295#note_160691

Fix based on Matthieu Vachon suggestion.
The problem is `timeout for git` != `timeout for satellite`. 

Satellite: 

* lock satellite
* clone or fetch repo
* cleanup and prepare remotes/branches
* do git call (one or several)
* cleanup and release lock 


As you see git call is only part of satellite. Having same value for satellite and git does not makes sense.

You can create separate config value for satellite timeout in [this section](https://github.com/gitlabhq/gitlabhq/blob/master/config/gitlab.yml.example#L197-L199)  if you want. But default value should be still 30 seconds because for most users bigger value does not makes sense.