Add a new helper method to log to error
Add a new helper method to log to error

Instead of just info, command output should go to stderr if there's an error.

PiperOrigin-RevId: 158151716
Change-Id: I945c237aaec37ab699c7a0b11e05843a92be8e07

google/copybara,google/copybara,google/copybara