migration: Extend migration_file_set_error() with Error* argument

Use it to update the current error of the migration stream if
available and if not, simply print out the error. Next changes will
update with an error to report.

Reviewed-by: Avihai Horon <avihaih@nvidia.com>
Acked-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
4 files changed