Curl polls an app over HTTP until it returns the expected "Powered by" banner.

Push executes a `git push deis master` from the current directory using the provided key.

PushUntilResult executes a `git push deis master` from the current directory using the provided key, until the command result satisfies expectedCmdResult of type model.CmdResult, failing if settings.DefaultEventuallyTimeout is reached first.

PushWithInterrupt executes a `git push deis master` from the current directory using the provided key, but then halts the progress via SIGINT.

StartPush starts a `git push deis master` command and returns the command session.