Fix RE unit test case. (#632)

Fix RE unit test case. (#632)

Unit test case which was failing:
RemoteResourceObjectTest.IsCachingReturnsTrueAfterStartCaching()

Reason for failure: Shared pointer reference for RCSRemoteResourceObject
was not released. Due to which, there was a problem in tearing down the test case.

This PR has the fix.
Additionally, application will receive caching callback
from RCSRemoteResourceObject only if remote resource object is available.

https://github.sec.samsung.net/RS7-IOTIVITY/IoTivity/pull/632
(cherry-picked from e8fb156d8239ace91f9529830f4781ea16e85bd3)

Change-Id: Idf587d1f5add4360a717a6959dcc839bc7aacb9f
Signed-off-by: Senthil Kumar G S <senthil.gs@samsung.com>
Signed-off-by: DoHyun Pyun <dh79.pyun@samsung.com>