Split image into dev and production flavors

[clemtibs]

Lean and mean for production, no ssh.

ssh and perhaps some other things for dev/testing.

[clemtibs]

At the moment, I'm doing a sort of "in-between". I'm leaving SSHD installed on the image which adds about 35mb, but it's not enabled by default. The daemon is only started when specifying the $GH_USER variable at run time. When the entrypoint.sh script in the radial/spoke-base container detects that it's set, it will download those keys and run ssh. I'm open to comments on this, but this seems to allow both easy testing/entry/debugging and then switchover to production without changing the image or rebuilding; just restarting without that env var.