[CP-7377] [CP-7376] Add HOSTTIME=utc option to installers

Added to installwizard.msi and citrixxendrivers*.msi

use argument HOSTTIME=utc for UTC hosttime,
or HOSTTIME=local for the default (treating xentime as local clock)

No hosttime argument will use whatever was previously set (and local
if nothing was previously set)

Signed-off-by: Ben Chalmers <Ben.Chalmers@citrix.com>