build: Enable security by default

build: Enable security by default

From now on, developer will need to disable security explicitly:
  scons SECURED=0

Bug: https://jira.iotivity.org/browse/IOT-1295
Change-Id: Ic09acf3996b47799020730fc34cd382325a981d8
Origin: https://gerrit.iotivity.org/gerrit/#/c/12073/
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/12073
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: George Nash <george.nash@intel.com>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Nathan Heldt-Sheller <nathan.heldt-sheller@intel.com>