v2v.tests: Adjust parameters for convert_local_image test.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
v2v.tests: Minor fix to convert_local_image module.

* Add debugging for test module.
* Make sure converted vm is down when cleanup.
* Change temp dir for pool from test.tmpdir to data_dir.TMPDIR.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>