Use primitive object while create nova client Server object

We need to use primitive object while create nova client Server object
instead of directly using nova.object.Instance object, because the
Server object construction will mess up the nova.object.Instance change
fields, that will result in the db updating operation will not update
the field like "updated_at".

Closes-Bug: #1365895
Change-Id: Ifc8e41c753b5fa2fa73d1eb1a4c02cdcec363460
(cherry picked from commit 4ca5fa32b1d676f085650de0c04b96f9da945ea8)