iotests: Make nbd-fault-injector flush

When closing a connection, make the nbd-fault-injector flush the socket.
Without this, the output is a bit unreliable with Python 3.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Reviewed-by: NCleber Rosa <crosa@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <20181022135307.14398-2-mreitz@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

tests/qemu-iotests/083.out

@@ -41,6 +41,7 @@ can't open device nbd+tcp://127.0.0.1:PORT/foo
 
 === Check disconnect after neg2 ===
 
+Unable to read from socket: Connection reset by peer
 Connection closed
 read failed: Input/output error
 
@@ -54,6 +55,7 @@ can't open device nbd+tcp://127.0.0.1:PORT/foo
 
 === Check disconnect before request ===
 
+Unable to read from socket: Connection reset by peer
 Connection closed
 read failed: Input/output error
 
@@ -116,6 +118,7 @@ can't open device nbd+tcp://127.0.0.1:PORT/
 
 === Check disconnect after neg-classic ===
 
+Unable to read from socket: Connection reset by peer
 Connection closed
 read failed: Input/output error
 
@@ -161,6 +164,8 @@ can't open device nbd+unix:///foo?socket=TEST_DIR/nbd.sock
 
 === Check disconnect after neg2 ===
 
+Unable to read from socket: Connection reset by peer
+Connection closed
 read failed: Input/output error
 
 === Check disconnect 8 neg2 ===
@@ -173,6 +178,8 @@ can't open device nbd+unix:///foo?socket=TEST_DIR/nbd.sock
 
 === Check disconnect before request ===
 
+Unable to read from socket: Connection reset by peer
+Connection closed
 read failed: Input/output error
 
 === Check disconnect after request ===
@@ -234,6 +241,8 @@ can't open device nbd+unix:///?socket=TEST_DIR/nbd.sock
 
 === Check disconnect after neg-classic ===
 
+Unable to read from socket: Connection reset by peer
+Connection closed
 read failed: Input/output error
 
 *** done

tests/qemu-iotests/nbd-fault-injector.py

@@ -112,6 +112,7 @@ class FaultInjectionSocket(object):
             if rule.match(event, io):
                 if rule.when == 0 or bufsize is None:
                     print('Closing connection on rule match %s' % rule.name)
+                    self.sock.flush()
                     sys.exit(0)
                 if rule.when != -1:
                     return rule.when