Use phutil functions to copy/move files
Use phutil functions to copy/move files

Summary:
The `cp` and `mv` commands, when run from a Windows
environment, error out.  Use library functions from `Filesystem`
for cross-platform compatibility.

Test Plan:
Ran `arc lint` with auto-fix lint errors on both Linux and
Windows.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Spies: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D16273

chundongwang/arcanist,folsom-labs/arcanist,aik099/arcanist,Khan/arcanist,uber/arcanist,phacility/arcanist,fivestars/arcanist,folsom-labs/arcanist,folsom-labs/arcanist,chundongwang/arcanist,codelabs-ch/arcanist,fivestars/arcanist,r4nt/arcanist,phacility/arcanist,uber/arcanist,codelabs-ch/arcanist,fivestars/arcanist,r4nt/arcanist,aik099/arcanist,Khan/arcanist,folsom-labs/arcanist,codelabs-ch/arcanist,codelabs-ch/arcanist,Khan/arcanist,chundongwang/arcanist,uber/arcanist,uber/arcanist,Khan/arcanist,chundongwang/arcanist,phacility/arcanist,fivestars/arcanist,r4nt/arcanist,phacility/arcanist,aik099/arcanist,codelabs-ch/arcanist,aik099/arcanist,r4nt/arcanist,phacility/arcanist