[services] Tests - Separate backup id from log id for pull backup

Summary:
Depends on D4246

After a separation of log/backup IDs in D4245, we need to distinguish them in the test code as well.

Test Plan:

cd services
yarn run-integration-tests backup

Reviewers: palys-swm, varun

Reviewed By: palys-swm, varun

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

Differential Revision: https://phab.comm.dev/D4376