custom ordering for TemplateBuilder images

[Alex Heneveld]

Hi folks,

I'd like to tie in to jclouds's TemplateBuilder so that I can use its 
filtering capabilities but then use custom logic to determine which of 
the matching images is "best" (for my custom value of best).

The driving use case is that I want a portable way to say "any recent 
ubuntu or centos".  Normally this is the default of course but it 
doesn't always do the right thing when other options are specified -- 
broken ubuntu "alpha" images in AWS being the worst offender (asking for 
16gb RAM in us-west-1 gives back an awful ubuntu 8.04 alpha, for 
instance!).  It would also handle use cases where someone says "Ubuntu 
11 or 12, or CentOS 6.x, is best. failing that, Ubuntu 10 or CentOS 5.x. 
(and never any alpha images!)".

I'm happy to add an issue and work on this but I wanted to check: does 
this look like a good idea?

In terms of the solution, I see two options:  TemplateBuilder could take 
an imageOrdering predicate where the builder applies my ordering 
(currently the Impl just uses a hard-coded DEFAULT_IMAGE_ORDERING); or 
we could make the existing Impl buildImagePredicate method public and 
let the user do the filtering then sorting.  Any preference?

Thanks
Alex