First pass at adding ability to make the VNC server view-only and password-protected,
for both types of displays. These can be set as parameters to the selenium::node::display
class. Eg.

class { 'selenium::node::display':
  enable_vnc       => true,
  vnc_view_only    => false,
  use_vnc_password => true,
  vnc_password     => 'secret'
}

By default, VNC displays will not be password protected, but they will be view-only.

The VNC password is stored plaintext on the node, in a file that can only be read by
the Selenium user.

Also, fixed two bugs:
  - headless displays were running as root, will now run as Selenium user
  - the headed display remote access settings were pretty broken -- sometimes, after the onlogin
    script was run, VNC would be enabled, other times not. It turns out that gconftool-2 is actually
    deprecated in Ubuntu 12. So, switched to gsettings, which is working way better.