kvm tools: Improve compat message format

kvm tools: Improve compat message format

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Before:
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*** Compatibility Warning ***

        virtio-blk device was not detected

While you have requested a virtio-blk device, the guest kernel did not initialize it.
Please make sure that the guest kernel was compiled with CONFIG_VIRTIO_BLK=y enabled in its .config

*** Compatibility Warning ***

        virtio-net device was not detected

While you have requested a virtio-net device, the guest kernel did not initialize it.
Please make sure that the guest kernel was compiled with CONFIG_VIRTIO_NET=y enabled in its .config

  # KVM session ended normally.

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After:
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  # KVM compatibility warning.
        virtio-blk device was not detected.
        While you have requested a virtio-blk device, the guest kernel did not initialize it.
        Please make sure that the guest kernel was compiled with CONFIG_VIRTIO_BLK=y enabled in .config.

  # KVM compatibility warning.
        virtio-net device was not detected.
        While you have requested a virtio-net device, the guest kernel did not initialize it.
        Please make sure that the guest kernel was compiled with CONFIG_VIRTIO_NET=y enabled in .config.

  # KVM session ended normally.

Signed-off-by: Asias He <asias.hejun@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>