$settings_dir mode to 0755; comment tweak

$settings_dir is situated in the shared folder, so Puppet's attempt to pound
mode 0775 are futile and generate noise on Puppet runs. This is probably a good
sign that the creation of the settings_dir should be the job of the role class.

This patch also tweaks a comment in Vagrantfile regarding Vagrantfile-extra.rb.

Change-Id: I5c3dac1eafa26f9d720b78ce07b90ed9730ee638