Fix citrix_hypervisor failing tests

[NouemanKHAL]

What does this PR do?

• Fixes the tests fixtures to be well-formed jsons.
• Removes the usage of yaml package to parse the response in favor of the response.json() method.

More info here: https://docs.xenserver.com/en-us/xenserver/developer/sdk-guide/using-http.html

Motivation

Fix failing test in the minimum_base_check job

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.98%. Comparing base (0965ff0) to head (92adca3).
Report is 1 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
citrix_hypervisor	86.75% <100.00%> (-0.71%)	⬇️
hive	?
hivemq	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
solr	?

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[AAraKKe]

I am wondering, why is it that we were not doing this before and now we can? I mean, we were loading it with yaml before for some reason right? Just making sure this is not going to fix tests but fail when running the integration with the real system. If we are covered by any integration/e2e I am ok with it.