Refactor test context creation to be less error-prone

[mattcary]

Follow-on to #2227, where conditionally creating a hyperdisk test context caused problems in waiting on a channel for those test contexts. Now we avoid that error-prone channel extraction by just writing in to the test context slices directly.

/kind failing-test

None

[k8s-ci-robot]

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[mattcary]

Converting to draft this time so that if the arm test fails it won't accidentally merge.

[mattcary]

/retest

[k8s-ci-robot]

@mattcary: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-gcp-compute-persistent-disk-csi-driver-verify	c4ad4d0	link	true	/test pull-gcp-compute-persistent-disk-csi-driver-verify
pull-gcp-compute-persistent-disk-csi-driver-e2e-windows-2022	c4ad4d0	link	false	/test pull-gcp-compute-persistent-disk-csi-driver-e2e-windows-2022

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