standalone_test: fix of getting type name from config path

@ client/tests/virt/ $ ./run -c qemu/cfg/tests.cfg
  IOError: [Errno 20] Not a directory: '/home/devel/
  autotest/client/tests/virt/cfg/cfg/virtio-win.cfg'

The processed type name is 'cfg', it should be 'qemu'

I tried to execute run without 'type' parameter,
and got an error of wrong path of cfg file.
This patches fixed this problem. 'options.type' is
also used in other part, so assign the processed
type name to it.

v2: fix a wrong assignment

Signed-off-by: Amos Kong <akong@redhat.com>