mirrord cli doesn't log when using RUST_LOG

[aviramha]

To reproduce:

RUST_LOG=mirrord=trace MIRRORD_PROGRESS_MODE=off mirrord exec sh

logs will start only from layer, not cli.
Bug seems to happen due to this code:

    // There are situations where even if running "ext" commands that shouldn't log, we want those
    // to log to be able to debug issues.
    let force_log = std::env::var("MIRRORD_FORCE_LOG")
        .ok()
        .and_then(|s| s.parse().ok())
        .unwrap_or(false);

    if force_log || init_ext_error_handler(command) {
        tracing_subscriber::registry()
            .with(tracing_subscriber::fmt::layer().with_writer(std::io::stderr))
            .with(tracing_subscriber::EnvFilter::from_default_env())
            .init();
    }

[linear]

MBE-729 mirrord cli doesn't log when using `RUST_LOG`