compute_ctl: don't panic if control plane can't be reached (#10078)

## Problem

If the control plane cannot be reached for some reason, compute_ctl
panics

## Summary of changes

panic is removed in favour of returning an error.
Code is reformatted a bit for more flat control flow

Resolves: #5391

compute_tools/src/bin/compute_ctl.rs

@@ -246,47 +246,48 @@ fn try_spec_from_cli(
     let compute_id = matches.get_one::<String>("compute-id");
     let control_plane_uri = matches.get_one::<String>("control-plane-uri");
 
-    let spec;
-    let mut live_config_allowed = false;
-    match spec_json {
-        // First, try to get cluster spec from the cli argument
-        Some(json) => {
-            info!("got spec from cli argument {}", json);
-            spec = Some(serde_json::from_str(json)?);
-        }
-        None => {
-            // Second, try to read it from the file if path is provided
-            if let Some(sp) = spec_path {
-                let path = Path::new(sp);
-                let file = File::open(path)?;
-                spec = Some(serde_json::from_reader(file)?);
-                live_config_allowed = true;
-            } else if let Some(id) = compute_id {
-                if let Some(cp_base) = control_plane_uri {
-                    live_config_allowed = true;
-                    spec = match get_spec_from_control_plane(cp_base, id) {
-                        Ok(s) => s,
-                        Err(e) => {
-                            error!("cannot get response from control plane: {}", e);
-                            panic!("neither spec nor confirmation that compute is in the Empty state was received");
-                        }
-                    };
-                } else {
-                    panic!("must specify both --control-plane-uri and --compute-id or none");
-                }
-            } else {
-                panic!(
-                    "compute spec should be provided by one of the following ways: \
-                    --spec OR --spec-path OR --control-plane-uri and --compute-id"
-                );
-            }
-        }
+    // First, try to get cluster spec from the cli argument
+    if let Some(spec_json) = spec_json {
+        info!("got spec from cli argument {}", spec_json);
+        return Ok(CliSpecParams {
+            spec: Some(serde_json::from_str(spec_json)?),
+            live_config_allowed: false,
+        });
+    }
+
+    // Second, try to read it from the file if path is provided
+    if let Some(spec_path) = spec_path {
+        let file = File::open(Path::new(spec_path))?;
+        return Ok(CliSpecParams {
+            spec: Some(serde_json::from_reader(file)?),
+            live_config_allowed: true,
+        });
+    }
+
+    let Some(compute_id) = compute_id else {
+        panic!(
+            "compute spec should be provided by one of the following ways: \
+                --spec OR --spec-path OR --control-plane-uri and --compute-id"
+        );
+    };
+    let Some(control_plane_uri) = control_plane_uri else {
+        panic!("must specify both --control-plane-uri and --compute-id or none");
     };
 
-    Ok(CliSpecParams {
-        spec,
-        live_config_allowed,
-    })
+    match get_spec_from_control_plane(control_plane_uri, compute_id) {
+        Ok(spec) => Ok(CliSpecParams {
+            spec,
+            live_config_allowed: true,
+        }),
+        Err(e) => {
+            error!(
+                "cannot get response from control plane: {}\n\
+                neither spec nor confirmation that compute is in the Empty state was received",
+                e
+            );
+            Err(e)
+        }
+    }
 }
 
 struct CliSpecParams {