Fixed broken observation cancellation.

Fixed broken observation cancellation.

Observe Cancel was broken because the uri from the client callback was
not copied into the request object. This caused connectivity to eat the
request witout sending it out.

Change-Id: Ib0ab815647897f2815fdffc3011e9977a003ac5f
Signed-off-by: Mandeep Shetty <mandeep.shetty@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1637
Reviewed-by: Omkar Hegde <omkar.m.hegde@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>