test: fallback to null if chart version not defined

[kb-newrelic]

Summary

• Fixes test: use testKey instead of host.name for nightly #378 which doesn't account for terraform erroring instead of using null for an undefined field of an object. The chart version is no defined for the host distro as it's using the local nr-backend chart which can't be used in a versioned way as its not published anywhere.
• Increasing nightly test timeout/retries as it failed for an ec2-based test. The EC2 got replaced in the deploy step before and expected telemetry was present during debugging, so test probably ran before EC2 fully spun out and started reporting. Second run (including increased timeout passed) - it might have succeeded without as well but this should increase the chance of it passing on the first try.

[mailo-nr]

LGTM