`dir_mode` is not supported on Windows

[myii]

While looking at #205, came across:

users-formula/users/init.sls

Line 225 in 8d48adb

- dir_mode: 700

• Refer back to: added dir_mode logic for users.user_files #205 (comment)

I don't have a Windows minion to test with but this hard-coded use of dir_mode will probably cause problems. It should be resolved in a similar way to #205, by making it opt-in via. pillar/config.

@arthurlogilab Would you mind looking into this?