B-428 B-436: rework virtual network template management

[treywelsh]

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Description

Rework virtual network template update

References

Close #428 Close #436

New or Affected Resource(s)

• opennebula_virtual_network

Checklist

• [ ] I have created an issue and I have mentioned it in References
• [ ] My code follows the style guidelines of this project (use go fmt)
• [ ] My changes generate no new warnings or errors
• [ ] I have updated the unit tests and they pass succesfuly
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have updated the documentation (if needed)
• [ ] I have updated the changelog file

[treywelsh]

There is more work than I expected initially:

I realized that there is some fields like gateway with a computed behavior, not sure they are useful, and by the way it seems that some reading code around Vnet template elements were missing. Here are the attributes I'm looking at for now in this PR: gateway, network_address, network_mask, search_domain, dns

[treywelsh]

Seems I can't use TestCheckNoResourceAttr to test gateway attribute removal in state, so, in place I test for an empty value: resource.TestCheckResourceAttr("opennebula_virtual_network.test", "gateway", ""),

I already used TestCheckNoResourceAttr but for values stored inside of a container type, or for the container type itself (TypeSet, TypeList, TypeMap...)

There is an other problem: in adding missing reading code for gateway, network_address, network_mask, search_domain, dns, acceptance tests fails for virtual network reservation: The reservation seems to inherits attributes from it's parent network. To solve this I'll ignore these attributes at read step when reservation_vnet is set.

My initial idea was to do something similar to the virtual machine resource when it inherit the attributes from a template with the template_tags section (i.e. keep elements from the template resource to avoid reading them in virtual machine code when they are inherithed but not configured). But finally it's a bit more than needed for this particular case.