Changes exit status for heat_network unit test
Changes exit status for heat_network unit test

If the test fails, it should exit the script not the cluster. Just
reporting this error and gracefully exiting the script should be
sufficient. My reasons for this are:

    * The tests are not completely reliable to say if the cluster is
      broken for sure.
    * The tests are not meant to fix the issues with the cluster, it
      could be a packaging issue or bug in the product. Our aim is
      not to catch them.
    * If there is a problem with heat, the other servies are still
      running fine. And the cluster is still usable.

Change-Id: I246bd3144189eba69a64ad545e6fe123e310595e

dguitarbite/OpenStack-Labs,openstack/training-labs,openstack/training-labs,dguitarbite/OpenStack-Labs,dguitarbite/OpenStack-Labs,openstack/training-labs