Add option to install imaging and load balancing services

This merge would close https://github.com/eucalyptus/eucalyptus-cookbook/issues/62.

I'm not actually super happy with the layout of this patch.  

On the one hand, I don't want to just install the imaging and load balancing services by default, because (a) not everyone needs them, and (b) together they add half an hour to the install.

So for now, they're an option for CIAB installs (*not* NC installs). When the install is complete, the user is asked if they want to install the additional services. If they say yes, the installation of the new services proceeds; if they say no, it doesn't. Either way, the configuration proceeds normally at that point.

Have a look. Again, the patch isn't super pretty, but it does the job.  If you think it's good to merge as is, go for it. :)