GitUtil: Add real FS only when cloning over ssh
GitUtil: Add real FS only when cloning over ssh

The TODO about removing SSH from tests is overly optimistic: one caller,
SshPushForReviewIT, is explicitly about testing the SSH codepaths, and
will continue to exist for the foreseeable future. We can still avoid it
in the non-SSH case, however.

Change-Id: I99f78abd42a7189f42a57d1f22414d7523ab23f0

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