trace: trace bdrv_open_common()

bdrv_open_common() is a useful point to trace since it reveals the
filename and block driver for a given BlockDriverState.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

block.c

@@ -475,6 +475,8 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
 
     assert(drv != NULL);
 
+    trace_bdrv_open_common(bs, filename, flags, drv->format_name);
+
     bs->file = NULL;
     bs->total_sectors = 0;
     bs->encrypted = 0;