connection failure errors on FacilityAdminCredentialsForm are handled like auth failures

[jonboiser]

Observed behavior

Unable-to-connect errors (e.g. peer went offline suddenly) are displayed as "invalid credential" errors because of the catch-all error handling.

This should be an edge-case because the UI tries to disable peers that are offline, making it hard to get to this state to begin with.

Expected behavior

1. invalid credential errors and unable to connect errors are handled differently (with different messages)

A possible message would be "This device is offline"

User-facing consequences

Errors and logs

Steps to reproduce

1. Start an import-facility workflow with a peer
2. After getting to the credentials form, turn off that peer
3. Enter the correct credentials and press "submit"
4. Get the in accurate "invalid credentials" error

Context

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