Rename downstream functions and variables
Rename downstream functions and variables

This patch renames downstream_callback to schema_rollback_cb and
downstream_to to schema_timeout to match the name with functionality.

CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source