Update a logic for POST request in Enrollee implementation

Update a logic for POST request in Enrollee implementation

Updated logic/flow:
(1) Parsing the requested attribute like tnn, cd, and tr
(2) Check if the provisioning is completed
(3) Check if the trigger is requested
(4) If the trigger process fails due to some reason, revert an attribute tr
    to 0

Change-Id: I1db3bfcd3b0d5593516b7719d64ba23f831ba9bc
Signed-off-by: Jihun Ha <jihun.ha@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/8075
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>