Don't check "repository.default-local-path" for readability in a cluster environment

Summary:
Ref T2783. When repository services are defined, skip the check for local repository storage.

In particular, in the Phacility cluster, this path won't exist on web nodes, but nothing will ever try to access it.

Test Plan: Verified new branch gets hit with cluster services defined.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2783

Differential Revision: https://secure.phabricator.com/D11100