Create list_snapshot_images.rb

Provide a method for retrieving snapshot images.
Update list_images.rb

Comments were copied from list_flavors.rb, correcting documentation link
Update images.rb
Update images.rb
Delete list_snapshot_images.rb
Update list_images.rb
Merge pull request #2087 from dJason/patch-4

Create Compute::RackspaceV2::Real.list_snapshot_images