scsi-disk: scsi-block device for scsi pass-through should not be removable

This patch adds a new SCSI_DISK_F_NO_REMOVABLE_DEVOPS feature. By this
feature we can set that the scsi-block (scsi pass-through) device will still
be removable from the guest side, but from monitor it cannot be removed.

Cc: qemu-stable@nongnu.org
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>