Update Order models

This CR updates the Order models to use the revamped Orders API.  There
are two concrete Order classes: KeyOrder and AsymmetricOrder which can
be used to create typed orders with types 'key' and 'asymmetric'
respectively.

Change-Id: I0bfb221d1ee00ae3e26be77afc32c7da9cbc59ca
Remove unnecessary try/except in container delete

It appears that the keystone sessions no longer trap the server error
responses in an undesirable way, so this is not necessary anymore.

Change-Id: Id73593535803fe589b317be923ad469cc0c3682b