virttest.virsh: Add APIs for vol-clone and vol-wipe

Signed-off-by: Yanbing Du <ydu@redhat.com>
Merge pull request #1478 from will-Do/vol_api

virttest.virsh: Add APIs for vol-clone and vol-wipe
data_dir: Add target parameter fo get_deps_dir()

With this parameter, get_deps_dir() will only deps folder
which contains target file/folder.

Signed-off-by: Feng Yang <fyang@redhat.com>