Commit c22a0345 QAPIfied option parsing in the NFS block driver, but
forgot to remove all the options we processed. Therefore, we get an
error in bdrv_open_inherit(), which thinks the remaining options are
invalid. Trying to open an NFS image will result in an error like this:

    Block protocol 'nfs' doesn't support the option 'server.host'

Remove all options from the QDict to make the NFS driver work again.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 20180516160816.26259-1-kwolf@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>