Add /oic/d and /oic/p discovery response messaging to IoTivity.

Add /oic/d and /oic/p discovery response messaging to IoTivity.

Prior to this, Clients could only perform a GET request directly on
/oic/d and /oic/p. This commit also enables performing DISCOVERY
requests on /oic/d and /oic/p as well.

This aligns with OIC spec compliancy.

This fixes Jira Ticket IOT-874.

Change-Id: I29693a67bb245b3fae8d1ed54833eacd1397884e
Signed-off-by: Joseph Morrow <joseph.l.morrow@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4567
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Markus Jung <markus.jung85@gmail.com>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>