security: CA cert arrives in publicData

security: CA cert arrives in publicData

GetCaCert must pick up this cert from the publicData of the credential
sent by CTT/OBT, rather than optionalData.

This behavior is clarified by OCF Security WG CR1938.

This patch allows CT1.7.8.5: DTLS handshake to make progress. The
handshake still fails later on, for different reasons that are being
investigated.

Change-Id: I76962e9f116ad7acb80a6da6c85fb089ebba3481
https://jira.iotivity.org/browse/IOT-2621
Signed-off-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/21983
Reviewed-by: Kevin Kane <kkane@microsoft.com>
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Nathan Heldt-Sheller <nathan.heldt-sheller@intel.com>