[GOCA] migrate xml package from xmlpath to encoding/xml

[treywelsh]

Description
The goal of this migration is to use the encoding/xml package instead of xmlpath in order to decode the XML content from OpenNebula.
For each OpenNebula entity, a set of structures will be defined to which is directly mapped the XML content.
The developper will work directly with theses structures.
Sometimes due to dynamic parts he will have to do some tests but less than with xmlpath module.

The types conversions and parsing part are removed from the developper code,
in this way, his code will be much more simple, and this also allow auto completion.

Use case
It's useful for every XXX.info requests.

Interface Changes
This does not modify functions prototypes, but add a bunch on structures that the developer can use directly.

Additional Context
I'll provide a pull request soon.

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

[treywelsh]

Some bug has been found by the ONE team in my code so I reopen this case and provide a pull request to fix this.

Add:

• Info method struct cleaning
• remove some mutualized part among structs, it cost a bit more of memory but the code is less tricky...