clarify CentOS version command can be run on
The command is not the same for CentOS 6 and 7 but the current wording makes it sound like it is. This fixes that.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
The command is not the same for CentOS 6 and 7 but the current wording makes it sound like it is. This fixes that.