Tweak provisioning unittest sconscript

Tweak provisioning unittest sconscript

New version (addressing [IOT-2396]) was pushed, which undid some of
  the "new" formatting style, restore
Refactor slightly, use src_dir and out_dir which are already
  defined, instead of re-fetching from env
Define an action for Popen on separate line, for readability

Change-Id: Id90944a50d7ec626d2e29a1822208c67b2c7b438
Signed-off-by: Mats Wichmann <mats@linux.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/21165
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>