Introduction of --nc switch

The --nc switch will install a node controller only, instead of the full cloud-in-a-box stack.  Invocation is as follows:

bash <(curl -s https://raw.githubusercontent.com/gregdek/eucalyptus-cookbook/master/faststart/cloud-in-a-box.sh) --nc

When the patch is accepted, invocation will be from eucalyptus/eucalyptus cookbook instead.

Please review this patch closely. I've tested in gregdek/eucalyptus-cookbook, and both ciab path and nc path work for me.  Accepting this means risk for the current live CIAB, so want to make sure it's solid.