Updating the fields that are copied from instances.

The list of fields copied from instances when creating the bless /
launched instance has grown stale. Some of the fields have been
removed from nova's database (e.g. state_description), some have
been renamed (e.g. launch_time->launched_at) and some fields have
been added (e.g. architecture).

Fixes OS-210.

Change-Id: I6d6840602c8606677414284051ecfc9d324334c9