Minor mods to commands for installUsbLib and uninstallUsbLib tasks.

Hi Javi!

I'm back from vacation, and I updated to the latest code.  I tried the new grunt build scripts for linux and they exited early with a couple of errors involving creation or deletion of a directory.  Adding a couple of flags to the commands fixed things.

I'm not sure if this is where the latest code is.  If it isn't, let me know and I'll put the pull request to the appropriate place.