Crowbar crashes after deploying existing node back to crowbar

[hgaikwad]

Description:
Crowbar crashes after deploying existing node back to crowbar

Version/Build: mesa-1.6_openstack-os-build.3508.dev

Browsers Used: IE11.0

Reproduction Steps:

1. Install crowbar.
2. After crowbar installation, start adding nodes to the crowbar server network.
3. The nodes would PXE boot and show up into the node dashboard for deployment.
4. Select a node and click on Delete.
5. The node would be deleted from the node list.
6. Now boot up the same node using PXE to the same network.
7. The node would again start PXE booting to be discovered under the nodes.
8. However, before the discovery completes, the crowbar crashes with the message "We're sorry, but something went wrong."

Observed Results:
Crowbar crashes after deploying existing node back to crowbar

Expected Results:
Crowbar should not crash with addition of a pre-existing node back to crowbar

Impact:
The user would have to restart crowbar