Allow callers of AllProjectsCreator to control the commit message

Callers may want to use a shorter fixed message that does not
include the version number. Allow the caller to control the
text as they see fit, falling back to the default standard
message if not specified.

Change-Id: I25648ea24fd46c54e2c1ca28553ee1c393ebde8c
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