Move and generalize decorator serialize_args to nova.objects.base

It would be nice use decorator `serialize_args` as general-use
decorator. Note that this single-purpose decorator was covering
up our ability to drill down to the actual method implementation
for hash calculation in the TestObjectVersions test. This patch
also enhances the decorator to be transparent, and makes the
test able to drill down through multiple layers of decorators
to find the actual implementation.

Co-Authored-By: Dan Smith <dansmith@redhat.com>
Change-Id: Ie454bffba113d7b3a863e975b2fb0ee6fb1dd552
Merge "Move and generalize decorator serialize_args to nova.objects.base"