shell: rework code to use shell.spawn

spawn gives out streams and we have more control over the stdout/stderr
buffers. otherwise, we have to provide a max buffer capture size to exec

src/database.js

@@ -146,7 +146,7 @@ async function exportToFile(file) {
     assert.strictEqual(typeof file, 'string');
 
     // latest mysqldump enables column stats by default which is not present in 5.7 util
-    const mysqlDumpHelp = await shell.exec('/usr/bin/mysqldump --help', {});
+    const mysqlDumpHelp = await shell.spawn('/usr/bin/mysqldump', ['--help'], { encoding: 'utf8' });
     const hasColStats = mysqlDumpHelp.includes('column-statistics');
     const colStats = hasColStats ? '--column-statistics=0' : '';