jenkins: Clean up AMI maintenance scripts

Remove the agent-setup-script.sh and linux-init.sh scripts,
because they're not used in the current workflows.

Rename build-ami.sh to build-amis.sh (since it builds all of them,
not just a single AMI) and add some comments about how to run.

Author: bwbarrett

jenkins/agent-setup-script.sh

@@ -1,9 +1,18 @@
 #!/bin/sh
 #
+# Copyright (c) 2017      Amazon.com, Inc. or its affiliates.  All Rights
+#                         Reserved.
+#
+# Additional copyrights may follow
+#
 # Build a new set of AMIs for Jenkins using Packer.  This script
 # requires packer be installed, along with the packer.json and
 # customize-ami.sh scripts in this directory.
 #
+# Run this script from your laptop using an IAM role for the
+# ompi-aws-prod account with EC2 priviledges or from aws.open-mpi.org
+# using the instance's role.
+#
 
 OPTIND=1
 packer_opts=""