Fix marker pagination for /servers
Fix marker pagination for /servers

Fixes bug 1053028.

Recent changes to pagination required passing in full sqlalchemy objects
into paginate_query. However, calls to paginate_query were passing in
strings.

Change-Id: Ib1396a78a12aef1a9cdc31f3624af30f19da44b5

citrix-openstack-build/oslo.versionedobjects,openstack/oslo.versionedobjects