shell: set utf8 encoding explicity for spawn and as the default for sudo

src/shell.js

@@ -152,6 +152,8 @@ async function sudo(tag, args, options) {
          options.stdio = ['pipe', 'pipe', 'pipe', 'ipc'];
     }
 
+    if (!options.encoding) options.encoding = 'utf8'; // better error message output
+
     const spawnArgs = [ ...sudoArgs, ...args ];
     return await spawn(tag, SUDO, spawnArgs, options);
 }