Convert qemu-img create to new bdrv_create

This patch changes qemu-img to actually use the new bdrv_create interface. It
translates the old-style qemu-img options which have been bdrv_create2
parameters or flags so far to option structures. As the generic approach, it
introduces an -o option which accepts any parameter the driver knows.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>