Reformat SConstruct to Python code style

Reformat SConstruct to Python code style

This is the last important build script that did not get reformatted:
  clarify some things in comments
  4-space indents
  python style: should use "is" and "is not" comparisons to None
  use clearer test for service/java depend (java_build was just calculated)
  use list-of-dirs form to call list of projects

Bug: https://jira.iotivity.org/browse/IOT-1745
Change-Id: Id260c2e55d62cb824d1e23e62df4ca8df5ce2b80
Signed-off-by: Mats Wichmann <mats@linux.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/21157
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: George Nash <george.nash@intel.com>
Reviewed-by: Pawel Winogrodzki <pawelwi@microsoft.com>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>