qemu: backup: integrate with blockpull
qemu: backup: integrate with blockpull

Merge the bitmaps when finalizing a block pull job so that backups work
properly afterwards.

https://bugzilla.redhat.com/show_bug.cgi?id=1799010

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@redhat.com>

olafhering/libvirt,olafhering/libvirt,nertpinx/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,crobinso/libvirt,nertpinx/libvirt,jardasgit/libvirt,crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,jardasgit/libvirt,jfehlig/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,jardasgit/libvirt,nertpinx/libvirt,jardasgit/libvirt,olafhering/libvirt,nertpinx/libvirt,nertpinx/libvirt,crobinso/libvirt,jardasgit/libvirt,libvirt/libvirt,zippy2/libvirt,crobinso/libvirt,zippy2/libvirt,zippy2/libvirt