[docs] a small update on RELEASING.adoc
[docs] a small update on RELEASING.adoc

Minor clarification on the username to use for logging in at
gerrit.cloudera.org to update gerrit mirroring configuration.  Also,
fixed formatting of the numbered sub-list and added an item to verify
that gerrit has been restarted successfully.

Change-Id: I3046e24b63b1d70a0e5f4d5d28b5335a26255137
Reviewed-on: http://gerrit.cloudera.org:8080/14411
Tested-by: Kudu Jenkins
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu