fixes #3832 - foreman supplies user for GCE images, fog expects username
(cherry picked from commit 51908af77554e588e85f7a6f73f1ce3e15aa4157)
fixes #3832 - foreman supplies user for GCE images, fog expects username
(cherry picked from commit 51908af77554e588e85f7a6f73f1ce3e15aa4157)