block: introduce bdrv_get_block_status API

For now, bdrv_get_block_status is just another name for bdrv_is_allocated.
The next patches will add more flags.

This also touches all block drivers with a mostly mechanical rename.  The
sole exception is cow; because it calls cow_co_is_allocated from the read
code, we keep that function and make cow_co_get_block_status a wrapper.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/vmdk.c b/block/vmdk.c
index 9f82c45..23b4954 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1042,7 +1042,7 @@
     return NULL;
 }
 
-static int coroutine_fn vmdk_co_is_allocated(BlockDriverState *bs,
+static int64_t coroutine_fn vmdk_co_get_block_status(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors, int *pnum)
 {
     BDRVVmdkState *s = bs->opaque;
@@ -1837,7 +1837,7 @@
     .bdrv_close                   = vmdk_close,
     .bdrv_create                  = vmdk_create,
     .bdrv_co_flush_to_disk        = vmdk_co_flush,
-    .bdrv_co_is_allocated         = vmdk_co_is_allocated,
+    .bdrv_co_get_block_status     = vmdk_co_get_block_status,
     .bdrv_get_allocated_file_size = vmdk_get_allocated_file_size,
     .bdrv_has_zero_init           = vmdk_has_zero_init,