* op-challenger: Use a wrapper to specify the vm type for metrics

Decouples the vm type from the trace type to give the run-trace subcommand more flexibility, allowing it to report separate metrics for cannon and mt-cannon.

Also adjust the run-trace loggers to consistently use `mt-cannon` as the type.

* Use constant.
Co-authored-by: Inphi <mlaw2501@gmail.com>

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Co-authored-by: Inphi <mlaw2501@gmail.com>