[services] Backup - Send log - add reactor state mutex
Summary:
Depends on D3647
Adding a mutex for reactor's methods. The reason for this is explained in the comments.
Test Plan:
cd services yarn run-backup-service
Reviewers: palys-swm, geekbrother
Reviewed By: palys-swm
Subscribers: ashoat, palys-swm, Adrian, atul, benschac, yayabosh
Differential Revision: https://phabricator.ashoat.com/D3648