Bug Fix in earlier rehandhsake implementation

Bug Fix in earlier rehandhsake implementation

Identified a corner case in earlier rehandshake implementation where if
no data transfer takes place between client and Server before re-handshake
is issued, re-handshake process was failing. DTLS state machine does not
update it's state at Server until the first data packet was received from
client. Updated logic to detect for 're-handshake' situation when epoch
mis-match happens. Also updated dtls-client test app to conveniently test
the feature. Use 'client:rehandshake' command for testing.

Change-Id: Idfaad7d477508603c35ad7948ca7c8f05e3228d0
Signed-off-by: Sachin Agrawal <sachin.agrawal@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/349
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sudarshan Prasad <sudarshan.prasad@intel.com>
Reviewed-by: Chul Lee <chuls.lee@samsung.com>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>