Add an option to control unmounting on success in Etcher CLI (#362)

Signed-off-by: Juan Cruz Viotti <jviottidc@gmail.com>

lib/cli/cli.js

@@ -103,6 +103,12 @@ module.exports = yargs
       describe: 'confirm non-interactively',
       boolean: true,
       alias: 'y'
+    },
+    unmount: {
+      describe: 'unmount on success',
+      boolean: true,
+      alias: 'u',
+      default: true
     }
   })
   .argv;

lib/cli/etcher.js

@@ -57,7 +57,7 @@ form.run([
   return writer.writeImage(options._[0], {
     device: answers.drive
   }, {
-    unmountOnSuccess: false,
+    unmountOnSuccess: options.unmount,
     validateWriteOnSuccess: options.check
   }, function(state) {