test.volume_application: Check parameters before running.

Put parameters in config-file may cause preprocess error.
So move them to test module and check cdrom before running.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
tests.volume_application: Fix bugs.

 * Parted device in vms is optional because parted command
   may not exist.
 * Disk volumes couldn't be created in disk pool, so create
   them before create_volumes(...).
 * Pools will be in busy if we do not detach them on vms.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #183 from yumingfei/fix_volume_application

tests.volume_application: Fix pool problems and check cdrom.