Add Nethermind integration tests (#3100)

## Proposed Changes

Extend the current Geth merge integration tests to support Nethermind.

testing/execution_engine_integration/src/build_utils.rs

@@ -0,0 +1,73 @@
+use crate::SUPPRESS_LOGS;
+use std::env;
+use std::fs;
+use std::path::{Path, PathBuf};
+use std::process::{Command, Output, Stdio};
+
+pub fn prepare_dir() -> PathBuf {
+    let manifest_dir: PathBuf = env::var("CARGO_MANIFEST_DIR").unwrap().into();
+    let execution_clients_dir = manifest_dir.join("execution_clients");
+
+    if !execution_clients_dir.exists() {
+        fs::create_dir(&execution_clients_dir).unwrap();
+    }
+
+    execution_clients_dir
+}
+
+pub fn clone_repo(repo_dir: &Path, repo_url: &str) -> bool {
+    Command::new("git")
+        .arg("clone")
+        .arg(repo_url)
+        .arg("--recursive")
+        .current_dir(repo_dir)
+        .output()
+        .unwrap_or_else(|_| panic!("failed to clone repo at {}", repo_url))
+        .status
+        .success()
+}
+
+pub fn checkout_branch(repo_dir: &Path, branch_name: &str) -> bool {
+    Command::new("git")
+        .arg("checkout")
+        .arg(branch_name)
+        .current_dir(repo_dir)
+        .output()
+        .unwrap_or_else(|_| {
+            panic!(
+                "failed to checkout branch at {:?}/{}",
+                repo_dir, branch_name,
+            )
+        })
+        .status
+        .success()
+}
+
+pub fn update_branch(repo_dir: &Path, branch_name: &str) -> bool {
+    Command::new("git")
+        .arg("pull")
+        .current_dir(repo_dir)
+        .output()
+        .unwrap_or_else(|_| panic!("failed to update branch at {:?}/{}", repo_dir, branch_name))
+        .status
+        .success()
+}
+
+pub fn check_command_output(output: Output, failure_msg: &'static str) {
+    if !output.status.success() {
+        if !SUPPRESS_LOGS {
+            dbg!(String::from_utf8_lossy(&output.stdout));
+            dbg!(String::from_utf8_lossy(&output.stderr));
+        }
+        panic!("{}", failure_msg);
+    }
+}
+
+/// Builds the stdout/stderr handler for commands which might output to the terminal.
+pub fn build_stdio() -> Stdio {
+    if SUPPRESS_LOGS {
+        Stdio::null()
+    } else {
+        Stdio::inherit()
+    }
+}