qemu: monitor: Detect list of bitmaps from 'qcow2' format specific data

qemu: monitor: Detect list of bitmaps from 'qcow2' format specific data

We currently probe dirty block tracking bitmaps by looking at the loaded
ones ('dirty-bitmaps'). Unfortunately those may not yet be populated on
incoming migration when the image was not yet activated, but we need to
know which ones are stored in the image so that we don't migrate those
explicitly, which would fail.

Load the list of bitmaps in a qcow2 image from the format specific data,
which is already loaded at that point.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>