backend: Fix timezone on import of Windows VMs

Incorrect default timezeone was being set based on uninitialized osId.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1123809
Change-Id: I61197951a3ea7e0aeb1a10a7f11e7cbefd9d99fe
Signed-off-by: Martin Betak <mbetak@redhat.com>