Created SConscripts for the C and C++ unit tests.

Created SConscripts for the C and C++ unit tests.

This change included making mods to <src_dir>/resource/SConscript to:

-call the C and C++ unit test SConscripts

-ensure that the Google Unit Test library and Hippo Mocking
library were installed in <src_dir>/extlibs.

Also made a mod to ocstack.c/OCInit( ) to check for invalid mode parameter
and to stacktests.cpp to change OCDoResource signature for CA.

Change-Id: I290d04a876de8c99076e71827d91b5216ffaf29e
Signed-off-by: Doug Hudson <douglas.hudson@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/292
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sudarshan Prasad <sudarshan.prasad@intel.com>
Reviewed-by: Sashi Penta <sashi.kumar.penta@intel.com>