qcow2: Add refcount_bits to format-specific info

Add the bit width of every refcount entry to the format-specific
information.

In contrast to lazy_refcounts and the corrupt flag, this should be
always emitted, even for compat=0.10 although it does not support any
refcount width other than 16 bits. This is because if a boolean is
optional, one normally assumes it to be false when omitted; but if an
integer is not specified, it is rather difficult to guess its value.

This new field breaks some test outputs, fix them.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/qcow2.c b/block/qcow2.c
index e04ba6d..5c92803 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2482,7 +2482,8 @@
     };
     if (s->qcow_version == 2) {
         *spec_info->qcow2 = (ImageInfoSpecificQCow2){
-            .compat = g_strdup("0.10"),
+            .compat             = g_strdup("0.10"),
+            .refcount_bits      = s->refcount_bits,
         };
     } else if (s->qcow_version == 3) {
         *spec_info->qcow2 = (ImageInfoSpecificQCow2){
@@ -2493,6 +2494,7 @@
             .corrupt            = s->incompatible_features &
                                   QCOW2_INCOMPAT_CORRUPT,
             .has_corrupt        = true,
+            .refcount_bits      = s->refcount_bits,
         };
     }