Use @ instad of _ in predefined roles

Change-Id: I2e30b0b457b05d6674ed7e1182f855ee7c0d2532
Reviewed-on: http://review.couchbase.org/43663
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>