[FIX] runbot: update dependency repo before checkout

At checkout time when a build has no server (e.g. enterprise),
the dependency repo that contains the server needs to be extracted too.
It happens that this dependency repo is not up to date.

With this commit, the dependency repo is updated before its extracttion.

runbot/models/build.py

@@ -553,6 +553,7 @@ class runbot_build(models.Model):
                         'Building environment',
                         'Server built based on commit %s from %s' % (commit_oneline, closest_name)
                     )
+                    repo._update_git(force=True)
                     repo._git_export(closest_name, build._path())
 
                 # Finally mark all addons to move to openerp/addons