Added the find_images_by_name() method.

This allows you to locate an image by specifying part of its name. The
search is done in a case-insensitive manner.

For example, if 'cs' represents the nova client, you can find all Ubuntu
images by calling:

    ubu_imgs = cs.find_images_by_name("ubun")

It support regular expressions, so if you wanted all PVHVM Ubuntu
images, you can call:

   ubu_phhvm_imgs = cs.find_images_by_name("ubu.+pvhvm")