block: per caller dirty bitmap

Previously a BlockDriverState has only one dirty bitmap, so only one
caller (e.g. a block job) can keep track of writing. This changes the
dirty bitmap to a list and creates a BdrvDirtyBitmap for each caller, the
lifecycle is managed with these new functions:

    bdrv_create_dirty_bitmap
    bdrv_release_dirty_bitmap

Where BdrvDirtyBitmap is a linked list wrapper structure of HBitmap.

In place of bdrv_set_dirty_tracking, a BdrvDirtyBitmap pointer argument
is added to these functions, since each caller has its own dirty bitmap:

    bdrv_get_dirty
    bdrv_dirty_iter_init
    bdrv_get_dirty_count

bdrv_set_dirty and bdrv_reset_dirty prototypes are unchanged but will
internally walk the list of all dirty bitmaps and set them one by one.

Signed-off-by: Fam Zheng <famz@redhat.com>

---
v2: Added BdrvDirtyBitmap [Paolo]
qapi: Change BlockDirtyInfo to list

We have multiple dirty bitmaps in BDS now, switch QAPI to allow query
it (BlockInfo.dirty_bitmaps), and also drop old BlockInfo.dirty.

Signed-off-by: Fam Zheng <famz@redhat.com>
qapi: Add (Since 1.8) to BlockInfo.dirty-bitmaps

Signed-off-by: Fam Zheng <famz@redhat.com>