Fixed the checked_guard/nil_guard to pass by reference

Fixed the checked_guard/nil_guard to pass by reference

This fix should allow checked_guard to properly pass by
reference rather than pulling everything out to a copy.  This
should ensure that out parameters are possible in the C++ stack,
though still extremely discouraged.

Change-Id: Ide35e9eb7adbdd532f375f341286387a641e8436
Signed-off-by: Erich Keane <erich.keane@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2087
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>