restapi: Make OsType enum consistent with OsRepository

The restapi enum OsType contained WINDOWS_2008R2 which was not one of
the os' supported in OsRepository (only the windows_2008r2x64 is
supported).

Change-Id: I636de81217db51aaf122d0851f9102e7406e8531
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1109546
Signed-off-by: Martin Betak <mbetak@redhat.com>