win,msi: create npm folder in AppData directory

Create the empty npm folder in Roaming\Appdata so that non-Administrator
users have a place to store global packages. This fixes the error Error:
ENOENT, stat error that occurs when a user tries to run the npm install
<package> command.

Bug: https://github.com/joyent/node/issues/8141
PR: https://github.com/joyent/node/pull/8838


Reviewed-by: Bert Belder <bertbelder@gmail.com>

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