Fix and Add join/leaveGroup function for stability.

Fix and Add join/leaveGroup function for stability.

We provided leaveGroup in Thingsmanager.
But it has obscurities.
So, we have to separate two leaveGroup functions which
it had different arguments.

Now, We can select join/leaveGroup function to match our situation.

Change-Id: I0a570a4685e833e4e55ced50e1f37971b7076b26
Signed-off-by: HyunJun Kim <hyunjun2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/522
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>