loadtest: db cluster instance gets destroyed and re-created on ltctl create

Description

It looks like https://github.com/mattermost/mattermost-load-test-ng/pull/345 introduced this.
On a second call to ltctl create the cluster instance might get assigned to a different zone and terraform will destroy the existing one and create new one without warning.

QA Test Steps

No testing required.

Mana

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Assignee

Claudio Costa

QA Assignee

Lindy Isherwood

Reporter

Claudio Costa

Epic Link

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Mattermost Team

Platform

Sprint

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