api: Convert schemaTests to use vdsmapi.get_api

Change-Id: I3e5716fcb9724621f4fb282746bf02958b1972d4
Signed-off-by: Adam Litke <agl@us.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/12108
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>