adding python to *.py package calls

  - under windows we had the problem that *.py needs to be registered and
    even if we had it: a call with modified PATH variable resulted in
    strange two PATH variables in the environment (not sure that this was
    a problem of nmake or something else)
  - added -u to get the output unbuffered

Change-Id: I9326a31fc39a95b61d92bb00549f536db04af985
Reviewed-by: Matti Paaso <matti.paaso@digia.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>