test: make CreateInventoryInfo return an error

[karlkfi]

Instead of a panic, have CreateInventoryInfo and invWrapperFunc return an error, and then check the error in the tests calling these functions.

Take this oportunity to make all the calls more consistent.

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This pull-request has been approved by: karlkfi

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[k8s-ci-robot]

@karlkfi: 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
cli-utils-presubmit-master-e2e	ea98d4a	link	true	/test cli-utils-presubmit-master-e2e
cli-utils-presubmit-master-stress	ea98d4a	link	true	/test cli-utils-presubmit-master-stress

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