add functions to requestor classes for GET request

add functions to requestor classes for GET request

add requestGet function to scene list/collection/member requestors
to get attributes

Change-Id: I9be7e28686ab882b7f8a1562f9767983f586bba5
Signed-off-by: Minji Park <minjii.park@samsung.com>
Signed-off-by: jyong2.kim <jyong2.kim@samsung.com>
Signed-off-by: Minji Park <minjii.park@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/5097
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>