vdsm-tool upgrade-networks fails with KeyError: 'defaultRoute'

Issue

• Unable to start vdsmd service after host upgrade to RHEL 7.5

#journalctl -xe
<hostname> vdsm-tool[8874]: if attrs['defaultRoute']:
<hostname>  vdsm-tool[8874]: KeyError: 'defaultRoute'  <<========
<hostname>  systemd[1]: Failed to start Virtual Desktop Server Manager network restoration.
-- Subject: Unit vdsm-network.service has failed
-- Defined-By: systemd
-- Support: http:
-- 
-- Unit vdsm-network.service has failed.
-- 
-- The result is failed.
<hostname>  systemd[1]: Dependency failed for Virtual Desktop Server Manager.
-- Subject: Unit vdsmd.service has failed
-- Defined-By: systemd
-- Support: http:
-- 
-- Unit vdsmd.service has failed.
-- 
-- The result is dependency.
<hostname>  systemd[1]: Dependency failed for MOM instance configured for VDSM purposes.
-- Subject: Unit mom-vdsm.service has failed
-- Defined-By: systemd
-- Support: http:
-- 
-- Unit mom-vdsm.service has failed.
-- 
-- The result is dependency.
<hostname>  systemd[1]: Job mom-vdsm.service/start failed with result 'dependency'.
<hostname>  systemd[1]: Job vdsmd.service/start failed with result 'dependency'.
<hostname>  systemd[1]: Unit vdsm-network.service entered failed state.
<hostname>  polkitd[1636]: Unregistered Authentication Agent for unix-process:8835:35319 (system bus name 
<hostname>  systemd[1]: vdsm-network.service failed.