fix(image_to_vm): Add missing call to check_gsutil_opts.

The --upload_path argument was not being properly handled because this
was missing, creating lots of 54.0.0+2013-08-28-1810 style directories
instead of master. Oops.
Merge pull request #99 from marineam/master

fix(image_to_vm): Add missing call to check_gsutil_opts.