EA-1158/CP-5965: Use VDI UUID instead of minor in tapdisk-pause

Use the VDI UUID instead of the minor number for the tapdisk-pause plugin.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
EA-1158/CP-5965: Use nbd<pid>.<uuid> istead of just nbd.<uuid>

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
EA-1158/CP-5965: Replace minor with UUID in lcache

Also, replace missed minor with UUID in tapdisk-pause.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
EA-1158/CP-5965: Remove unused method rdev

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
EA-1158/CP-5965: Remove some references to blkback.

Remove some reference to blkback. This also removes some of the
functionality.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
EA-1158/CP-5965: Use NBD for IntelliCache.

Since there's no block device any more, use the parent's NBD.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
EA-1158/CP-5965: Fix tapdisk cache stats script

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>