Only add 'groups' file to the repo if it exists

The 'groups' file gets created only if there are groups mentioned in
the 'project.config' file.  A 'project.config' file is not required to
mention any groups, thus we should only attempt to add the 'groups' file
if it exists.

Change-Id: I333df5156bc27db29143ee412d86e12606faa751
diff --git a/jeepyb/cmd/manage_projects.py b/jeepyb/cmd/manage_projects.py
index 0e73585..b248e7d 100644
--- a/jeepyb/cmd/manage_projects.py
+++ b/jeepyb/cmd/manage_projects.py
@@ -247,10 +247,10 @@
         with open(group_file, 'w') as fp:
             for group, uuid in uuids.items():
                 fp.write("%s\t%s\n" % (uuid, group))
-    status = git_command(repo_path, "add groups")
-    if status != 0:
-        log.error("Failed to add groups file for project: %s" % project)
-        raise CreateGroupException()
+        status = git_command(repo_path, "add groups")
+        if status != 0:
+            log.error("Failed to add groups file for project: %s" % project)
+            raise CreateGroupException()
 
 
 def make_ssh_wrapper(gerrit_user, gerrit_key):