If can't build Docker image because disconnected, handle correctly

[davidpanderson]

Describe the bug

If a Docker job starts while host is disconnected, image creation will fail.
Detect this particular type of failure, and do a temporary exit.

Ideally there should be a variant of temporary exit that says:
retry when we have a network connection

Steps to reproduce

No response

Expected behavior

No response

Screenshots

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System information

No response

Additional context

No response

[davidpanderson]

Notes:
Docker uses HTTPS to fetch images.

Plan:

• docker_wrapper parses the output of the create image command, checking for an error indicating lack of physical network connection (as opposed to e.g. image doesn't exist).
• If so it does temporary_exit(), indicating that it's waiting for a physical connection (need to add this mechanism)
• The client flags the job as waiting for physical connection.
• If any network op succeeds, the client clears this flag, and the job can be restarted
• If a job is in this state, the client pings the reference site every 10-30 or so min