Stack migration suggests 'git push heroku master' even when that is not appropriate

[mmcgrana]

The console output of `heroku stack migrate suggests at the end:

-----> Migration prepared.
       Run 'git push heroku master' to execute migration.

Even when the heroku remote does not point to the app being migrated. If the user blindly follows this suggestion then they may get a git push error or inadvertently re-deploy the wrong app.

[ddollar]

The gems just displays the output of PUT /apps/APPNAME/stack, this will need to be changed in core.

[calvinfroedge]

So what do we do to finish the migration?