iotests: Make _filter_nbd drop log lines

The NBD log lines ("/your/source/dir/nbd/xyz.c:function():line: error")
should not be converted to empty lines but removed altogether.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/083.out

@@ -51,7 +51,6 @@ no file open, try 'help open'
 
 === Check disconnect after neg2 ===
 
-
 read failed: Input/output error
 
 === Check disconnect 8 neg2 ===
@@ -66,42 +65,34 @@ no file open, try 'help open'
 
 === Check disconnect before request ===
 
-
 read failed: Input/output error
 
 === Check disconnect after request ===
 
-
 read failed: Input/output error
 
 === Check disconnect before reply ===
 
-
 read failed: Input/output error
 
 === Check disconnect after reply ===
 
-
 read failed: Input/output error
 
 === Check disconnect 4 reply ===
 
-
 read failed: Input/output error
 
 === Check disconnect 8 reply ===
 
-
 read failed: Input/output error
 
 === Check disconnect before data ===
 
-
 read failed: Input/output error
 
 === Check disconnect after data ===
 
-
 read 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
@@ -132,7 +123,6 @@ no file open, try 'help open'
 
 === Check disconnect after neg-classic ===
 
-
 read failed: Input/output error
 
 *** done

tests/qemu-iotests/common.filter

@@ -237,7 +237,7 @@ _filter_nbd()
     # receive callbacks sometimes, making them unreliable.
     #
     # Filter out the TCP port number since this changes between runs.
-    sed -e 's#^.*nbd/.*\.c:.*##g' \
+    sed -e '/nbd\/.*\.c:/d' \
         -e 's#nbd:127\.0\.0\.1:[^:]*:#nbd:127\.0\.0\.1:PORT:#g' \
         -e 's#\(exportname=foo\|PORT\): Failed to .*$#\1#'
 }