Fix result of notification valgrind memory checker.

Fix result of notification valgrind memory checker.

When valgrind of notification service(including cpp wrapper) is run,
several leak was detected. (memory leak and invalid use of memory)

in this patch, result of valgrind was fixed.
1. invalid use of string in the unit test code, was fixed.
2. when returnning with error, allocated memory was freed.
3. unfreed variable was freed.
4. unit test build warning was fixed.

Change-Id: I4c8367bfda86813bb1ce1c71cf7841067c489ccc
Signed-off-by: KIM JungYong <jyong2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/19009
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>