add username (or other identifier) to pod name and/or label by default

[kolia]

from @hannahilea

...when doing kubectl get pods it can be hard to know which pods are ones that I've started (and can therefore kill) vs ones other people might be running. Throwing a username into the name could alleviate this.

from @kolia

Could use a particular env var such as JULIA_POD_USERNAME and default to "$(whoami)" if that is not set? That way usage stays terse (just julia_pod.)

from @soulshake

(Extra credit if this can be made a label on the created pods so you can use a selector to filter them for deletion etc)

[kolia]

Partially addressed by #12, which adds git_repo, git_branch and git_sha labels to the job and pod.

For convenience, the label selectors you can use get logged before dropping into the julia repl.