Updating the googlecompute builder documentation.

Update post-processor.html.markdown

Fixed some typos in the interface{} mentions.

Update virtualbox-iso.html.markdown

Changed type to virtualbox-iso

Fixes #806 Build fails if GOPATH has multiple paths

website: includes information about "provider"

none

website: really fix puppet provisioner cmd docs

builder/docker: include user vars for docker configuration

builder/virtualbox-ovf: fix shutdown_timeout handling

The shutdown_timeout config parameter was being ignored
(for both the user setting and the "5m" default) on the
virtualbox-ovf builder. As a result, packer complained
of timeouts on graceful shutdowns, and the build process
would error out. This fixes that along with some newly
created tests.

website: correct default puppet provisioner command

Documentation/docker: link pointing to dockerfiles was incorrect