Print full error with stacktrace, if compute node startup fails.

It failed in staging environment a few times, and all we got in the
logs was:

    ERROR could not start the compute node: failed to get basebackup@0/2D6194F8 from pageserver host=zenith-us-stage-ps-2.local port=6400
    giving control plane 30s to collect the error before shutdown

That's missing all the detail on *why* it failed.

compute_tools/src/bin/compute_ctl.rs

@@ -157,7 +157,7 @@ fn main() -> Result<()> {
             exit(code)
         }
         Err(error) => {
-            error!("could not start the compute node: {}", error);
+            error!("could not start the compute node: {:?}", error);
 
             let mut state = compute.state.write().unwrap();
             state.error = Some(format!("{:?}", error));