Fixed collections double-sending children IOT-652

Fixed collections double-sending children IOT-652

The children in a collection were being added both during
resource-conversion and during collection conversion.  This fixes this
by making sure that resources don't add their children in cases where
they are not collections.

Change-Id: I1da7f98ddcc2c0a66a30165785e46cee83b77b5d
Signed-off-by: Erich Keane <erich.keane@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2200
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Omkar Hegde <omkar.m.hegde@intel.com>