Fix change directory for WinRM protocol

Summary: Ref T2015.  The WinRM protocol changes directories while still under cmd.exe (before jumping into PowerShell).  As such, when the leased directory is a different drive, we need to make sure we change the current drive before running the command or else it will run from the wrong directory.

Test Plan: Tested in production.

Reviewers: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D10776