Improve instance verification for deploy

[javivelasco]

In the current version, we are printing the building logs when deploying and then exiting once the deployment state changes to READY. This makes one miss the logs of instances when they are being run so that we would be missing any potential boot failures. Also, we are printing a verification success message per instance in a function that is duplicated across commands.

With this PR we are introducing a new verifyDeploymentScale async generator function that yields a tuple [dc: string, instances: number] when the scale requirements of a DC are met for a deployment. Also, it extracts the event stream from the events generator so we can resume logging after we marked the deployment as a build success .

Finally, it updates alias and scale to use the same verification function.