shell: exec encoding is utf8 by default and no shell

explicitly mark calls that require the shell

src/system.js

@@ -68,7 +68,7 @@ async function hdparm(file) {
 }
 
 async function getSwaps() {
-    const [error, stdout] = await safe(shell.promises.exec('getSwaps', 'swapon --noheadings --raw --bytes --show=type,size,used,name', { encoding: 'utf8' }));
+    const [error, stdout] = await safe(shell.promises.exec('getSwaps', 'swapon --noheadings --raw --bytes --show=type,size,used,name', {}));
     if (error) return {};
 
     const swaps = {};
@@ -329,7 +329,7 @@ async function getLogs(unit, options) {
 }
 
 async function getBlockDevices() {
-    const result = await shell.promises.exec('getBlockDevices', 'lsblk --paths --json --list --fs', { encoding: 'utf8' });
+    const result = await shell.promises.exec('getBlockDevices', 'lsblk --paths --json --list --fs', {});
     const info = safe.JSON.parse(result);
     if (!info) throw new BoxError(BoxError.INTERNAL_ERROR, `failed to parse lsblk: ${safe.error.message}`);