Windows instances require the timezone to be "localtime"

This was relatively simple to fix, assuming that the image used
to boot the windows instance has the os_type set to "windows".
The use of os_type in this manner is consistent with the
existing use in the Xen hypervisor driver.

DocImpact: if you're booting windows instances, then you need to
set the os_type image property in glance to "windows". Otherwise
your instances will have their clock timezone set to UTC, which
has unexpected side effects in windows.

Change-Id: Id6759a290ed25c9add97ac61bb7d165b3fb908b2
Closes-Bug: 1231254
Merge "Windows instances require the timezone to be "localtime""