Handle running fetch_config more than once

The logic before assumed we'd be in a fresh repo - but we are no longer.
So change the logic to use -B which will remake and reset the branch,
which is actually what we want.

Change-Id: Ic216999b68bec5fb22acef3c5c1f09e49532e5c4
diff --git a/jeepyb/cmd/manage_projects.py b/jeepyb/cmd/manage_projects.py
index 23b121f..0a22f11 100644
--- a/jeepyb/cmd/manage_projects.py
+++ b/jeepyb/cmd/manage_projects.py
@@ -132,7 +132,7 @@
         return False
     # Because the following fails if executed more than once you should only
     # run fetch_config once in each repo.
-    status = git_command(repo_path, "checkout -b config "
+    status = git_command(repo_path, "checkout -B config "
                          "remotes/gerrit-meta/config")
     if status != 0:
         log.error("Failed to checkout config for project: %s" % project)