Handle \r character in Packer logs

[cb372]

Ansible does some fancy-pants logging in which it overwrites the line using \r. Currently we print this in a rather unsightly way:

(Reading database ... (Reading database ... 5% (Reading database ... 10% (Reading database ... 15% (Reading database ... 20% (Reading database ... 25% (Reading database ... 30% (Reading database ... 35% (Reading database ... 40% (Reading database ... 45% (Reading database ... 50% (Reading database ... 55% (Reading database ... 60% (Reading database ... 65% (Reading database ... 70% (Reading database ... 75% (Reading database ... 80% (Reading database ... 85% (Reading database ... 90% (Reading database ... 95% (Reading database ... 100% (Reading database ... 58006 files and directories currently installed.)

We could avoid this if we implemented proper support for \r, i.e. delete everything from the start of the current line to this point.