Launch Cluster - required dropdown with no choices should have better instruction

[Cindy Lu]

You need to have Cluster Template and Base Image defined before you can create cluster. However, a new user may not know this and just see that there are no selections or any explanation for what to do. When they click 'Create' they will just get the generic error msg 'This field is required.'

We need to make it clear that they need to take some actions beforehand.
We could have a '+' button beside the Base Image to link to "register an image" action, just like what Key Pair has?

http://docs.openstack.org/developer/sahara/horizon/dashboard.user.guide.html#launching-a-cluster

Related to: https://bugs.launchpad.net/horizon/+bug/1391343

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/135256

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/135256
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=bff8f1ba96b65bfd794c78895531148fac0da6f4
Submitter: Jenkins
Branch: master

commit bff8f1ba96b65bfd794c78895531148fac0da6f4
Author: nikunj2512 <email address hidden>
Date: Tue Nov 18 17:36:37 2014 +0530

    Improves Launch Cluster model in Data Processing panel

    This patch adds the '+' button next to the "Cluster Template" &
    "Base Image" which will help end users to add a cluster template
    or image from the "Launch Cluster" modal itself.

    Closes-bug: #1392851

    Change-Id: I26575675d32a8fd746022d0ea0dc9546f83e74cd