Without conflicting over the name of the launch template that they create/delete.
Previously, the launch template name was just hard coded to `packer-fleet-launch-template`, but since AWS enforces unique template names within an account, this caused simultaneously running packer instances to hit template-already-exists errors when creating their templates and race-conditions around deleting the template. Now, the template name is randomly generated on each run, so there should be no conflicts.
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