Only create All-Projects ACL once

If refs/meta/config already exists do not overwrite or update it
with default configuration. This protects site administrators who
run `java -war gerrit.war init -d /some/existing/site --batch` and
corrupt ACLs of a live server with default settings.

To really set the default ACLs on an existing site the admin
should remove the refs/meta/config branch so it can be created.

Change-Id: I44a21b0c162812747ebcd50535709e8330dfbef8
1 file changed