do_plan_zone_updates could report if it's blocked on inventory propagation

[smklein]

omicron/nexus/reconfigurator/planning/src/planner.rs

Lines 1392 to 1399 in c698911

	if !zones_currently_updating.is_empty() {
	info!(
	self.log, "some zones not yet up-to-date";
	"sled_id" => %sled_id,
	"zones_currently_updating" => ?zones_currently_updating,
	);
	return Ok(report);
	}

This looks like it returns, but the report is empty. If we're blocked on this case, we should probably identify "why" in the planning report.