Added option to install PubSub emulator

[caleb-artifact]

This pull requests adds an installPubSubEmulator option to the google-cloud-cli feature.

        "installPubSubEmulator": {
            "type": "boolean",
            "default": false,
            "description": "Install the 'google-cloud-cli-pubsub-emulator'?"
        }

This pull request also fixes a bug that prevented the GKE Gcloud Auth Plugin from being installed when the installGkeGcloudAuthPlugin was set to true.

Comprehensive tests for the google-cloud-cli options were also added.