Mac: FileBasedLock does not work as expected on Mac

`FileBasedLock` relies on Windows specific behavior, and because the locking is not working as expected the functional tests are occasionally failing.

Examples:

https://mseng.visualstudio.com/VSOnline/_build/results?buildId=7054343&view=logs

https://mseng.visualstudio.com/VSOnline/VSOnline%20Team/_build/results?buildId=7047738&_a=summary&view=logs