Add vcd_catalog_vapp_template resource and data source for managing vApp Templates and deprecate vcd_catalog_item

[adambarreiro]

Overview

This PR adds the resource and data source vcd_catalog_vapp_template to be able to upload, manage and fetch vApp Templates. This resource and data source is very similar to the existing vcd_catalog_item, in fact the idea is to potentially deprecate the latter once other resources like vcd_vm and vcd_vapp_vm are adjusted to use vApp Templates instead of Catalog Items.

• This PR addresses the issue Convert catalog item resource into vApp template #502.
• This PR depends on Extend Catalog with vApp Template retrieval functions go-vcloud-director#495

Detailed description

As #502 mentions, current vcd_catalog_item implementation is an hybrid of Catalog Item and vApp Template. In order to decouple both concepts, this PR adds the resource and data source vcd_catalog_vapp_template which only considers vApp Templates.

As v3.8.0 doesn't break compatibility, vcd_catalog_item resource and data source specification and source code are preserved as-is with minor code changes that doesn't affect its behaviour.

vcd_catalog_item is NOT deprecated in this PR as it can still be used in the vcd_vm and vcd_vapp_vm resources. A new PR must be done to adjust these two resources and be able to deprecate vcd_catalog_item

• resource_vcd_catalog_vapp_template.go: New resource for vApp Template

• datasource_vcd_catalog_vapp_template.go: New data source for vApp Template

• catalogitem.go: Removed the comment stating that findCatalogItem should be changed, as there is findVAppTemplate instead (see "Other comments").

• filter_get.go: Created getVappTemplateByVdcAndFilter to be able to fetch vApp Templates by VDC instead of Catalog: getVappTemplateByCatalogAndFilter.

• vcd/config_test.go: Added required entry in configuration for a vApp Template present in NSX-T backed VDC: nsxtCatalogItem.

Other comments

• resource_vcd_catalog_vapp_template.go has a new function findVAppTemplate that behaves similarly to findCatalogItem (in fact it started as a clone).
  I must admit that I'm not very happy with the implementation of this function, as the resulting code is quite complex and hard to read. The situation here is that I tried to split it in little functions to reduce complexity and comply a bit more with SRP, but in exchange the vcd package got polluted with these tiny semantic functions that were not quite re-usable. So I finally decided to have this big function. Let me know your thoughts about this.

Testing

• All tests with tag catalog pass
• Tested manually resource/vcd_catalog_vapp_template and datasource/vcd_catalog_vapp_template
  • Data source with VDC and filters
  • Data source with Catalog and filters
  • Data source with VDC
  • Data source with Catalog
  • Resource CRUD
• Tested manually resource/vcd_catalog_item and datasource/vcd_catalog_item to avoid regressions
• Run acceptance tests on VCD 10.3.x
• Run acceptance tests on VCD 10.4.x

[Didainius]

A few inline comments. Looks good otherwise - just double check that catalog tests use NSX-T VDC and templates - this should save us refactoring headache in future and add to CDS testing.

[lvirbalas]

LGTM! Looking forward to the needed changes in VM to be able to deprecate the catalog item.