Error detecting vcenter networks

[mouyaq]

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Description
If there is a host in disconnected state into the cluster, networks may not be retrieved giving the error:

"undefined method `networkSystem' for nil:NilClass"

To Reproduce
Importing in OpenNebula 5.12 a cluster with a host in disconnected state.
After import the hosts if you want to import any network you will get this error:

"undefined method `networkSystem' for nil:NilClass"

Expected behavior
Should list the available networks in vcenter server.

Details

• Affected Component: vCenter driver
• Hypervisor: vCenter
• Version: OpenNebula 5.12 with vCenter 6.0

Additional context
Add any other context about the problem here.

Progress Status

• Branch created
• Code committed to development branch
• Testing - QA
• Documentation
• Release notes - resolved issues, compatibility, known issues
• Code committed to upstream release/hotfix branches
• Documentation committed to upstream release/hotfix branches

[mouyaq]

PR: #4931