Allow Tommy to cope with depth=2 timeout

Summary:
Per T1441, we added in D1794 support for multi-branch projects.

On cd.nasqueron.org, query the API with depth=2 times out.
To avoid that, perhaps make it a disabled by default optional setting.

To enable it, put a truthy value in JENKINS_MULTI_BRANCH environment variable.

This is a follow-up for 8d7e01d292da.

Test Plan: Browse https://infra.nasqueron.org/cd

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2833