`lctl` errors are not propagated

[spoutn1k]

lctl errors are silently discarded and the exporter returns empty output.

lustrefs-exporter/lustrefs-exporter/src/routes.rs

Lines 86 to 94 in d39f692

	pub fn lustre_metrics_output() -> Command {
	let mut cmd = Command::new("lctl");
	cmd.arg("get_param")
	.args(parser::params())
	.kill_on_drop(true);
	cmd
	}

lustrefs-exporter/lustrefs-exporter/src/routes.rs

Lines 204 to 208 in d39f692

	let lctl = lustre_metrics_output().output().await?;
	let mut lctl_output = parse_lctl_output(&lctl.stdout)?;
	output.append(&mut lctl_output);

We should log errors if nothing else.