Windows fixes
Strip carriage returns from end of lines in virtualbox/driver.go, fixing wait for virtualbox host shutdown.
Fix target upload directory path in communicator.go to use forward slashes.  (When running on windows path/filepath returns backslashes...which does not work when the target host is unix).
Merge branch 'master' into jstamerj/windows
Merge pull request #1 from jstamerj/jstamerj/windows

Jstamerj/windows
Merge pull request #218 from jstamerj/master

builder/virtualbox, communicator/ssh: fixes for running on windows