resource-encapsulation: Isolate unit_tests building

resource-encapsulation: Isolate unit_tests building

Previously gtest libs were propagated to shared libs:

  g++ -o .../resource-encapsulation/src/common/librcs_common.so \
  (...) \
  -lgtest -lgtest_main \
  -lc_common -llogger -ldl -lpthread -luuid -lrt -loc

Change-Id: I9bcaa39d8cd5e1166b2ec7d7ede14d44f79a476e
Bug: https://jira.iotivity.org/browse/IOT-1745
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20241
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Dave Thaler <dthaler@microsoft.com>
Reviewed-by: Ziran Sun <ziran.sun@samsung.com>
Reviewed-by: Gregg Reynolds <dev@mobileink.com>
Reviewed-by: Pawel Winogrodzki <pawelwi@microsoft.com>