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.
@randx The old commit with 600 as default timeout hardcoded was removed. Now a new commit, with unit tests, fetching the conf from Gitlab.config.satellites.timeout was made. The default setting is 30.