Improve usability of Group Interface API.

Improve usability of Group Interface API.

GetActionSetFromString function has memory leak.
So we fix memory leak and improve usability of the function.

We call two function, ExtractKeyValueFromRequest and BuildActionSetFromString
to extract key and value from requset and get ActionSet object from string.

Fix [IOT-283]

Change-Id: Ie13dcd0afc168632d9a53ad27182d15a55c3aca0
Signed-off-by: HyunJun Kim <hyunjun2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/308
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>