Don't use .scubainit when DOCKER_HOST is set
Don't use .scubainit when DOCKER_HOST is set

This commit better separates the remote vs. local execution logic.
When running a remote docker container (DOCKER_HOST is set), we don't do
any of the .scubainit stuff added in #13.

This fixes #17.

JonathonReinhart/scuba,JonathonReinhart/scuba,JonathonReinhart/scuba