Run now takes a context as well as a statebag. We'll assign the context
to the blank identifier to prevent namespace collisions. We'll let the
step authors opt-in to using the context.
`find . -iname "step_*.go" -exec gsed -i'' 's/func \(.*\)Run(/func \1Run(_ context.Context, /' {} \;`
If using a builder that has an http server set up for file transfer,
expose the connection info to the shell provisioner through the environment
variable PACKER_HTTP_ADDR.
Closes#2869
