Instead of manually building a list of all options from BDRVQcowState
values just reuse the options that were used to open the image.
qcow2_open() won't fully use all of the options in the QDict, but that's
okay.

This fixes all of the driver-specific options in qcow2, except for
lazy-refcounts, which was special cased before.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>