Skip some repository checks in cluster enviornments

Summary:
Ref T2783. Currently, the repository edit page does some checks agaisnt the local system to look for binaries and files on disk. These checks don't make sense in a cluster environment.

Ideally, we could make a Conduit call to the host (e.g., add something like diffusion.querysetupstatus) to do these checks, but since they're pretty basic config things and cluster installs are advanced, it doesn't seem super worthwhile for now.

Test Plan: Saw fewer checks in a cluster repo.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2783

Differential Revision: https://secure.phabricator.com/D11102