Give monkey EXTERNAL_STORAGE.

lib/roles/device.js

@@ -159,7 +159,10 @@ module.exports = function(options) {
         .then(function(port) {
           var log = logger.createLogger('device:remote:monkey')
           return adb.shellAsync(options.serial, [
-              'monkey'
+              // Some devices fail without an SD card installed; we can
+              // fake an external storage using this method
+              'EXTERNAL_STORAGE=/data/local/tmp'
+            , 'monkey'
             , '--port', port
             ])
             .then(function(out) {