Not all properties can be set globally, and the "appName" in the global case is currently defaulted to `--global`. This is okay because domain label names cannot start with hyphens, and all app names must be valid domain label names.
Moving verification of input to the earliest place is the best way to decrease the need to validate this further downstream.
Additionally, some of the existing checks were.... lacking :)
Rather than attempting to always extract the Procfile, reference the one that was extracted by the last deploy. This fixes issues where 'docker container cp' may fail intermittently for lord knows what reason.
Closes#4083
There are other places in the codebase that currently act on all apps or could benefit from being able to do so. Being able to run `common.RunCommandAgainstAllApps()` and get that for free will be a boon to implementing this functionality elsewhere.
