Refactor unit test linking

Refactor unit test linking

* Build an octbstack_test static library.
* Link test executables against aforementioned static library.
* Remove octbstack_test.def file.
* Light cleanup of various SCons scripts

Note: This patch also fixes an issue where the build would fail
when TEST=0 was specified on Windows.

Change-Id: Ied7457fd5857396f4ce32bff37380998d66adeff
Signed-off-by: David Antler <david.a.antler@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/12115
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Dave Thaler <dthaler@microsoft.com>