CSI: show a useful error for on schedule / job validation for incompatible task drivers

[tgross]

Task drivers like QEMU can't support CSI, so we should show a useful error to the operator when they try to schedule a job (or validate one), rather than erroring-out at the client.

[tgross]

I tested this out a bit and it looks like QEMU doesn't support host volumes either. But because there's no checking, the jobspec will let you configure it and it just won't work (the volume isn't mounted).

So I'm wondering whether we should add a new field to the Driver Capabilities struct so that we can test this as part of task driver fingerprinting. It would need to be backwards-compatible with existing fields, so maybe something like VolumeSupport as an enum that defaults to "all" but has a "host volumes only" (is that a thing?) and a "none" option.

[angrycub]

I believe that I ran into this with the java driver on macOS because it doesn't have FSIsolation as well.

[github-actions]

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