Fix clean build error.

Fix clean build error.

".sconsign.dblite" should be deleted before running any configuration
tests.  Furthermore, do not run configuration tests when running scons
'clean' or 'help' operations.

Change-Id: Iedd97533db808bd2ac401defb38fd5b672649d45
Signed-off-by: Caiwen Zhang<caiwen.zhang@intel.com>
Signed-off-by: Ossama Othman <ossama.othman@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/426
Reviewed-by: Erich Keane <erich.keane@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>