Fix a newline issue in "arc" workflows

Summary:
We end up with one too few newline here in some workflows, like arc land with unstaged changes.

Root issue here is that phutil_console_prompt|confirm lead with too much whitespace but that's a harder fix.

Test Plan: Saw reasonable whitespace.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11927