Add success message to instack-build-images
Add success message to instack-build-images

When image builds complete successfully, there's no obvious way to
know other than checking $?.  This adds an echo after the build
calls, which thanks to set -e should only be run if everything
completes successfully.

Change-Id: I4fac0b05b7340b12447f3a23747a2a347bc0d33f

eprasad/instack-undercloud,rdo-management/instack-undercloud,bcrochet/instack-undercloud,dmsimard/instack-undercloud,dpkshetty/instack-undercloud,rdo-management/instack-undercloud,dpkshetty/instack-undercloud,bcrochet/instack-undercloud,eprasad/instack-undercloud,dmsimard/instack-undercloud