Add missing remote_branch and pre_commit_script

Adding missing remote_branch and pre_commit_script parameters in the
default modulesync.yml. This is necessary for the post-merge hook[1] to
work.

[1] https://review.openstack.org/#/c/189216/

Change-Id: I5203e3c7b84c808bef61542efd2c4d973729b425

modulesync.yml

@@ -2,3 +2,5 @@
 namespace: openstack
 git_base:  ssh://proposal-bot@review.openstack.org:29418/
 branch: msync_automatic_update
+remote_branch: refs/publish/master/msync_automatic_update
+pre_commit_script: openstack-commit-msg-hook.sh