pvSCSI: Fix some issues

Hi, all,

I will post some patches in order to fix issues of pvSCSI driver.

1. HVM domain support.
2. Fix incorrect value of "sense_len" field in response packet.
3. Fix emulation logic of "REPORT LUN" command. (This fix relates to the issue James-san pointed out on 30 Nov.)
4. Disable backend driver removal functionality. (The functionality did not work well.)
5. HVM domain support. (unmodified_driver support)

Best regards,

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Jun Kamada