(#8660) Default config dir to %PROGRAMDATA% on Windows

The puppet install.rb script now defaults the config directory to
%PROGRAMDATA%\PuppetLabs\puppet\etc on Windows. This is more inline
with Windows best-practices, as this directory is used to store
application data across all users. The PROGRAMDATA environment
variable also takes into account alternate system drives, by using the
SYSTEMDRIVE environment variable.

Note that the Dir::COMMON_APPDATA constant is so named because it
corresponds to the CSIDL_COMMON_APPDATA constant, which on 2000, XP,
and 2003 is %ALLUSERSPROFILE%\Application Data, and on Vista, Win7 and
2008 is %SYSTEMDRIVE%\ProgramData.

This commit also updates puppet's default run_mode var and conf
directories when running as "root" to match the install script, and
fixes the spec test, which was looking in the Dir::WINDOWS directory.

Reviewed-by: Cameron Thomas <cameron@puppetlabs.com>