[IOT-1527] change public api about group resoure

[IOT-1527] change public api about group resoure

Change-Id: I8e372299b38b18c43a883ad29b9362eed16de70c
Signed-off-by: eunok.shin <eunok.shin@samsung.com>
Signed-off-by: yeonghun.nam <yeonghun.nam@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/13607
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jee Hyeok Kim <jihyeok13.kim@samsung.com>
(cherry picked from commit c5ef5fae4f08b1fcb9c5c3c6dc50b6798c3fe975)
Reviewed-on: https://gerrit.iotivity.org/gerrit/14547
Reviewed-by: Uze Choi <uzchoi@samsung.com>