Context ISO with old configuration on NIC detach

[vholer]

Description

In the past when NIC detach happened, the OpenNebula didn't refresh the contextualization CD-ROM. Currently, the CD-ROM is refreshed, but still with old (pre-detach)
NIC configuration.

E.g., see the CD-ROM change on NIC detach

Jan 29 09:08:01 debian10-280057 kernel: VFS: busy inodes on changed media or resized disk sr0
Jan 29 09:08:01 debian10-280057 kernel: VFS: busy inodes on changed media or resized disk sr0
Jan 29 09:08:02 debian10-280057 systemd[1]: Starting OpenNebula reconfiguration script...
Jan 29 09:08:02 debian10-280057 one-contextd[2249]: Started for type all to reconfigure

but, although we have detached NIC eth1, it's still on context.sh

...
ETH0_VROUTER_IP=''
ETH0_VROUTER_IP6=''
ETH0_VROUTER_MANAGEMENT=''
ETH1_CONTEXT_FORCE_IPV4=''
ETH1_DNS=''
ETH1_EXTERNAL=''
...

It's similar to NIC_ALIAS detach #3484, but in both casese I would more prefer if the all entries just wanishes, instead of putting there extra DETACH=YES hintgs.

To Reproduce

1. Attach NIC
2. Detach NIC
3. Check context.sh and find detached NIC parameters

Expected behavior
context.sh contains current configuration.

Details

• Affected Component: Core
• Version: 5.8 and up

Additional context
Ref. https://opennebula.zendesk.com/agent/tickets/14277

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

[rsmontero]

Note: Probably skip all DETACH=YES NIC's in context generation will fix the issues