chore: Call initDiskControllers() in GetTestCloud()

[edreed]

/kind cleanup

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:

This PR changes the GetTestCloud function to call initDiskControllers instead of (incompletely) initializing the disk controllers directly. This way, the disk controller methods like AttachDisk and DetachDisk can be used in unit tests and mocked.

Which issue(s) this PR fixes:

Special notes for your reviewer:

Release note:

`GetTestCloud` properly initializes the disk controller fields enabling them to be used in unit tests and mocked.

[coveralls]

Coverage decreased (-0.001%) to 79.611% when pulling 2a00ffa on edreed:edreed-init-disk-controllers-in-test-cloud into e428596 on kubernetes-sigs:master.

[feiskyer]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: edreed, feiskyer

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