[services] Backup - Print out errors in reactors

Summary:
Depends on D3533

I thought we may want to print out error messages in reactors to the stdout in services - for now, they're not visible.

Test Plan:

cd services
yarn run-backup-service

Reviewers: geekbrother, palys-swm, varun, jimpo

Reviewed By: palys-swm

Subscribers: ashoat, palys-swm, Adrian, atul, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3534