[Qemu-block] iotest 223 is flaky

[Alberto Garcia]

I can make it fail by running it a few times:

223 1s ... - output mismatch (see 223.out.bad)
--- tests/qemu-iotests/223.out       2019-02-08 17:25:15.584387100 +0200
+++ tests/qemu-iotests/223.out.bad     2019-03-05 18:05:16.855223976 +0200
@@ -92,9 +92,10 @@
 
 === Use qemu-nbd as server ===
 
-[{ "start": 0, "length": 65536, "depth": 0, "zero": false, "data": false},
-{ "start": 65536, "length": 2031616, "depth": 0, "zero": false, "data": true},
-{ "start": 2097152, "length": 2097152, "depth": 0, "zero": false, "data": 
false}]
+qemu-nbd: Failed to blk_new_open 'tests/qemu-iotests/scratch/t.qcow2': Failed 
to get shared "write" lock
+Is another process using the image [tests/qemu-iotests/scratch/t.qcow2]?
+qemu-img: Could not open 
'driver=nbd,server.type=unix,server.path=tests/qemu-iotests/scratch/qemu-nbd.sock,x-dirty-bitmap=qemu:dirty-bitmap:b':
 Failed to connect socket tests/qemu-iotests/scratch/qemu-nbd.sock: Connection 
refused
+./common.nbd: line 33: kill: (11122) - No such process
 [{ "start": 0, "length": 512, "depth": 0, "zero": false, "data": true},
 { "start": 512, "length": 512, "depth": 0, "zero": false, "data": false},
 { "start": 1024, "length": 2096128, "depth": 0, "zero": false, "data": true},

Berto